The cost to code and market a Twitter clone would be a tiny fraction of $45b. If the existing Twitter is so bad that Elon needs to buy it and save it, then the value of the userbase is low - particulary considering that the time cost for a user to switch is much lower than say a Myspace to FB shift. I am assuming that Elon is not this much of a dumbass - what am I missing here?
No it wouldn't. Literally tons of people would do it and plenty of competitors have tried or are trying.
Per the value of the userbase and the cost of switching: well look at some of the competitors I mentioned, the ones Joe Rogan and others flock too when they get a temporary Twitter ban, do they not return immediately after their ban is lifted?
The cost of code and marketing can't beat Twitter's network effect. Getting Elon, Joe, and plenty of other personalities to move also is no guarantee that even a slight portion of the userbase switches.