How can crypto exchanges avoid sending a 1099-B?

How do crypto exchanges evade the same level of responsibility/regulation of equity markets or banking?

Regulation, in general, is not the same thing as required tax reporting (or actual tax, for that matter).

Who is and is not required to do information reporting and in which cases is set out, usually in detail, in the law enacted by Congress, interpreted where necessary by regulations adopted by the Treasury department. IRS doesn't get to decide. The laws weren't written to explicitly include cryptocurrency exchanges, probably because they didn't exist when these laws were written and Congress isn't psychic or omniscient, and Treasury at least so far hasn't asserted they can be interpreted to do so.

Treasury does assert that the anti-money laundering laws (the old Bank Secrecy Act and the post-9/11 'USA PATRIOT' act) apply to cryptocurrency exchanges as 'money service businesses'

Is crypto tax enforcement entirely dependent on random, individual audits?

Not random; the only random audits IRS does are what is now called the National Research Program, and before 'restructuring' in 1998 was more straightforwardly called the Taxpayer Compliance Measurement Program. This does full 'audits' on a small random sample -- about 1 in 10,000 returns -- to allow statistical projection to the whole population. Because audits (formally 'examinations') are expensive, they otherwise try to focus based on estimates of 'audit potential' -- how much noncompliance they can find and assess (and hopefully collect) for a given amount of effort.

And they certainly do recognize cryptocurrency as such a 'potential' area. They also like to use less expensive methods to 'encourage' compliance, especially what are called 'soft letters'. Instead of manually analyzing your info in detail -- with checks to make sure they don't miss anything, because they're only allowed to examine a given return once -- they just send a computer-generated letter saying "we think maybe you didn't comply" and suggest they might audit; if the taxpayer responds by amending their return, they win at very low cost, and if not, they still have the choice to audit if they decide it's worth the cost. See https://www.irs.gov/newsroom/irs-has-begun-sending-letters-to-virtual-currency-owners-advising-them-to-pay-back-taxes-file-amended-returns-part-of-agencys-larger-efforts -- although the Taxpayer Advocate office, essentially an internal ombudsperson, considers this abusive; see https://www.taxpayeradvocate.irs.gov/wp-content/uploads/2020/08/JRC21_SAO_05.pdf . And people certainly have been receiving these letters; googling "IRS letter 6173" gets me "about 45,000 results".