My opinion is that, assuming Bitcoin's fundamentals remain strong, the primary factor is time. It's a matter of time until the long term bull market resumes.
The 2015-2017 era was an "accumulation and markup" period. The 2018-??? era is a "distribution and markdown" period. It's not so much about fundamental factors because the bubble and correction periods are dictated by speculation, not fundamentals. It's about the time it takes for speculators to have sold and exited the market. Eventually in any bear market, sellers become exhausted; everyone who plans to sell has already done so. That's what we're looking for, and it's not a matter of price or fundamentals. It's a matter of time.
It's not as simple as you make it seem, fundamentals are very important. Dec 2017 and peak numbers of trxs was a huge test of bitcoin scaling and it failed miserably. Trxs took days unless you paid like $25+ per trx, and even they they took hours. This is the main reason the price blew up imo, because this clearly showed the bitcoin network is not ready for prime time.
Wtf try again unless things have fundamentally changed regarding scaling? I honestly can't imagine another runnup without better fundamentals.
Maybe it represented failure to you, but the market saw it differently. There was actually a strong correlation between transaction fees and price on the run to $20K. Your position is based on the idea that users are unwilling to pay high fees for onchain transactions. I think we've seen strong evidence to the contrary. People are willing to pay high fees.
You're also only thinking about Bitcoin's use as a medium of exchange. That can partially be solved by the Lightning Network, which at this rate will be fairly robust by the time the next bubble comes around. Bitcoin also garners demand from speculative and store-of-value investors who don't necessarily mind paying high fees to buy and hold.