Why are options more popular than futures among retail investors?

These are just two products and not really an 'either-or' comparison; a little bit of apples and oranges. Still, there is some merit in looking at each product in the terms you've raised.

Options [These securities give one person the 'option' to buy or sell an underlying security at a specific price, for a specific period of time. If I buy an AAPL call option priced at $125 expiring Oct 31 2020, then I have 5 weeks to decide whether to exercise my right to buy a share of AAPL for $125, which I would only do if the share price in the market exceeded $125]

• Purchased options can be easily used to mitigate risk, because your downside is fixed to the initial purchase price. At the same time, upside may be 'unlimited', so you know what potential loss you are looking at, but can still reap significant rewards from price changes.

  [note: this thinking is dangerously close to gambling, not that all options are gambling, but I personally think someone susceptible to high-risk trading/gambling may trick themselves into thinking a call option is a 'sure thing' and continually lose money on purchase fees. This may particularly true for far 'out of the money' options, like say a $150 AAPL call option that expires in a few months that might cost only pennies, but theoretically there could be a long shot that price rises to, say, $155 making you $5 for just a few pennies, which would be a 10,000%+ return. You will often see options like this being touted on the near-notorious subreddit 'wallstreetbets', where naive amateur "investors" speculate on high risk investments]

• Calculation of pricing is not required to trade While the pricing of those options may be complex, if you assume at the outset that pricing for a particular market is reasonably efficient, then whatever price you see is 'fair', and you are therefore simply making a call [pun] on what direction you believe share price will go. This might mean someone can overpay for an option, but that is a risk with any uninformed trader getting in over their head. In some ways, because potential loss is defined, that risk is actually smaller with options. You see the wide price spreads on options as a sign that pricing may be incorrect, but it is not that simple, because there is asymmetric risk involved given one party takes upside potential for a fixed cost, and one party takes only downside risk for a fixed initial benefit.

• Further, combined options strategies can help to narrow in further on the risk/reward you are taking on, by zeroing in on when you would gain or lose money with that strategy. I assume much of the volume of information you are seeing on options is just building up step by step on the combined strategies that you might want to use. But using 'vanilla options' and just buying, say, a call option on a share that you expect will be volatile, doesn't require you to use those more advanced combinations at all.

Futures [These are derivatives of the commodities market, and effectively commit you to buy or sell an underlying commodity for a specific price at a specific point in time. If I buy a futures contract to purchase a barrel of oil for $100 in December 2021, then exactly 13 months from now, if I still hold the contract, I will owe the counterparty $100, and they owe me a barrel of oil. Some futures contracts require physical exchange of the actual underlying commodity, which investors avoid by selling their contracts for the value of the commodity at that time, before maturity to someone who actually does want the physical delivery.]

• Futures are more like 'regular equities' in that the investor holds both upside risk and downside risk. Potential loss can thus be larger.

• Use of margin accounts: Because you don't actually 'buy' anything initially, money doesn't change hands - you are basically making a bet on a future outcome, and your bet has theoretically no impact on the underlying price you are looking at. So no need to actually pay money to your broker, but if your 'bet' starts to look losing, you will need to fork money over to your broker, and they don't want to take on any risk that you won't pay, so you'll need to set up a margin account that defines what happens when your futures 'bets' start losing. This will likely be why you can't trade futures with Robinhood. [Partly because the margin accounts are part of the setup of a futures contract, use of leverage is more common, which itself can increase risk].

• In some cases, futures trading could require you to theoretically take physical possession of some assets, and therefore an inexperienced trader may not want to get into the area [though not all futures contracts have this implication, and you can usually sell before physical delivery occurs — see an interesting case on where this was a big problem for oil futures — How negative oil prices revealed the dangers of futures trading].

I would kindly suggest that if you think futures are 'simpler' than options, you may want to do more research before you start trading either. The two products are quite different from each other, and that difference should be something very definable if you really understand either one.