This is the main reason why I personally don't see the need of using bitcoin lending platforms. Sure, an extra 5-8% yield off your bitcoin(on top of the bitcoin value increase) can be quite sweet, but in exchange for handing over custody? Hell nah, I'm happy with my annual 2x-3x multipliers.
Yeah, I put a bit of Bitcoin onto BlockFi a few months ago to get that 6% gain, but they've adjusted it down almost every single month since then, but now I get under 2%. It's less than a tenth of my bitcoin in the first place, as wasn't willing to risk more than that on a centralized place, but since they've cut my earnings rate by two-thirds in the past few months I will probably just move that back to my own address by end of this year. 2% is not worth giving over custody. 6% maybe, but 2% is bullshit.
I think the reason why it went down was due to the GBTC premium. Most of the BTC they were borrowing was for GBTC so market makers could milk the premium. However when the premium disappeared and turned negative they got in trouble. Hence why they couldn't afford to pay the 6% or so. And 6% in my opinion was a rip off since they were making more than double it for your BTCs.
Whats popular is to lend USD and USDT however. Those historically (except bear markets) usually will yield you around 10% a year. So if you sold some crypto that you don't need. You can just lend it out for 10% instead of leaving it in your bank account to get 0.5% APY. However keep in mind there is still counterparty risks, You can't lend it while its in cold storage.
But it's great to have 2x-3x return annually rather than taking risks into other platforms or alts. Also, DCA will be the best strategy to grow our portfolio. 
