The inventor of the pet rock, Dahl, moved on after the hype to other adventures. SpaceX and Twitter are so deferent from Tesla and there is good chance neither will ever make what T-Bills could have.
Honestly the battery component of Tesla is needed for the US power grid, the overbuilding for Peak demands at the subdivision (100+) homes really is insane. If you can level 3-30 amps at 1200V volts to 6-12 amps the cost of buried and arial installs really goes away. Make that on something that gets dropped off like a shipping container and stuck in a corner someplace. Stanadarize the connectors for quick replacement, then 100 homes do not all “need” their own solution.
My impression is that Musk didn't purchase Twitter as a monetary investment but rather as an investment in mankind's future. Without free speech, things go downhill fast.
SpaceX is a private company. They make a lot of money on satellite launches but most of that goes into Starship and the expansion of the Starlink fleet.
I envision that the biggest moneymaker for Musk will eventually be Starlink. 10s of millions of subscribers paying at least $100 per month is a pretty hefty cash-flow.