Why is no routing number asked for?

my recipient gave me their routing number and account number.

This is typical for ACH transfers between accounts that you own, or wire transfers to other people. (Note that wire transfers are usually pretty expensive.)

However, the "pay bills" functionality of my online bank portal only asks for the recipient's account number and address.

Look for a QuickPay or Zelle feature from your bank, or maybe PayPal or the Cash app. However, they only require an email address or mobile phone number. (If the recipient is also new to the US banking system, he may also have made that mistake.)

Why does it not ask for any bank information or routing number?

Probably because it has a database of major (and mid-sized) companies that use EDI (Electronic Data Interchange).

There should be a method for paying a person or company which does not have EDI. In that case, though, they'd just ask for the person's name and address to mail them a check.

The bill pay feature at many banks is used to pay either a business or an individual.

If you are paying a business, the bank will usually ask for your account number with that business. For example, if you are paying an electric bill, the account number you're supposed to put there, is your account number with the power company. The bank will then include this information when they send the payment so that the power company can know what account to credit the payment to.

If you're paying an individual, then your bank will only ask for their name and address (and maybe their phone number). Then the bank will simply write a check made out to that person and mail it to the address you specified.

I think you're mistakenly working under the "pay a business" feature, when you should be working under the "pay an individual" feature of your bank's bill pay service; thus, the account number confusion.

If you want to pay your friend directly, then all you need is his name and address.

If you want to pay a bill for him, then you need the company the bill belongs to and your friend's account number on the bill. You will never need your friend's bank account nor routing number.

As mentioned above, they do indeed have databases, though it might take a brave (careeless) payor to be willing to assume the payee just from name similarity. There ARE more similarities available to raise the confidence of success though: the first coming to mind being the account number structure of different businesses being different, often, so even though there might be six electric companies with names similar enough, the account number structure you give (say, 182-996-736-2-3 or ###-###-###-#-#) could make it pretty certain a particular one is right. Your location might be a good second "similarity" and your checkwriting history with the payor (if a bank) might well be a solid third. Lots of others one wagers too. And they might even immediately send a query to all concerned and base their payment on the replies. Though none of that might be helpful for a payment to a florist.

More importantly, it is a cheap way for them to seek business and this likely plays a role. As a business, we receive payments like this perhaps 10 times a month (manufacturer, so not doing 12,000 transactions a month like a video store might (have)). And EVERY single one of them contains a "Come, COME TO ME little one, come to me and gain all the (non-)benefits of using this same service!" And EVERY last one of them contains a "Come to our website and sign up to receive these payments via ACH which will certainly not arrive sooner like we want to imply as we simply won't send them until later... but will be hideously cheaper for us than these paper... things... you are getting now!"

EVERY single one, even after receiving a dozen already.

So yeah, might be a paper check the first time or two, but they work hard on shifting you to sending the required information so they can ACH it. Why do they not just ask the originator? Well, getting that kind of information presents a barrier to entry, eh? Even a mild one is still a barrier. And there's no interacting via ACH so there is no obtaining the payee as a (probably bigger) user of the service.

And the other big reason for desiring the payee as a customer is that many of these services, and ALL of them that work through a credit card in some way or another, try to sell you on a credit line to float the checks. For many the lack of actual benefit and high costs vs. their own paper checks or ACH's is not a problem if credit they cannot otherwise obtain, or only obtain after climbing significant barriers to entry with, say, banks, is offered along with it.

Those markets are why these services make it as easy as possible, and then even easier, even dangerous, for the low-level payee to engage them. Costs are still minimal compared to possible gains.

And not one of them would EVER have the least problem holding your money a week or two trying to resolve a payment difficulty, then simply "returning" it (i.e.: NOT returning it, but netting it from their draw for some upcoming batch... of course), leaving you holding the bag and having to explain your mortgage payment not arriving, with late fees now tacked on and so on.

Like someone said though, the ACH system is hilariously antiquated. Not that it is the active reason for anything here, but it certainly limits the supply of these service providers to predators.