Largely long-time Bitcoin holders and smart ICOs. Anyone who's a real (not paper) Bitcoin millionaire probably got that way by selling near the peak. Ditto anyone whose salary has been paid by a crypto firm that collected millions in an ICO. Most of the engineers working for companies like Consensys, Brave, Filecoin/IPFS, etc. are indirect beneficiaries of the 2017 Bitcoin bubble.
The ICO boom had an interesting triple-pyramid-scheme structure that accelerated both the rise and the fall. If you bought into Ethereum in the early days, you probably paid with Bitcoin; it wasn't possible to buy ETH direct until ~2017. And similarly, if you bought into ICOs in 2017, you bought with ETH. That meant that the folks investing their money in ICOs weren't actually putting $200M into Filecoin; they were putting ETH that they had spent maybe $20M (in aggregate) in, which was likely purchased from someone who had bought it with $2M in Bitcoin. The eye-popping ICO valuations attracted more people into the market, which allowed smart ICOs to unload their ETH immediately at inflated prices and convert it into a big corporate war chest. Once the bubble popped, this mechanism worked in reverse (a bunch of dumb ICOs that had held onto their ETH all try to sell to capture the tiny pool of inflowing capital, which does nothing except force down the price of ETH), leaving folks who bought at the top of the bubble and ICOs that forgot to sell holding the bag.
Ironically, this mechanism holds the basics of a functioning financial system: money was transferred from people who weren't doing anything with it to pay salaries of people doing productive but speculative work. It was transferred pretty clumsily, with a lot of people losing their shirt and a fair bit of waste and scams in the receiving projects, but if any of the receiving projects deliver, it succeeded.