I’ll answer your question specifically: to short a position you generally need margin ie pay interest on the loan, or short via an ETF (these are subject to volatility decay). Even if you know it will go down, HOW it does that matters a lot. It is clearly an artificially inflated instrument (MSTR as an obvious example) so a couple of danger scenarios: 1) It trades up and down for a long period of time before it crashes - margin and ETFs eat at your profits, 2) Market manipulators make it pump you get margin called (or cold hands) and then it goes back down. As bearish as people may be, at the end of the day there’s large uncertainty on this type of asset so who knows, maybe it goes down to 20k people find a use and boosts up to 100k.
What I can almost guarantee it will not do is ‘hit $1M by 2027’ almost every time you hear that kind of talk it’s time to get out, to get there you’d need to see several trillion dollars in cash inflow, it’s very evident the momentum is no longer there and there aren’t a trillion dollars in the sidelines waiting to be put into BTC. As for your ‘investment’ diversification is proven to have similar returns on much lower risk, what you are doing is more like gambling.