A focus on Mars could itself bankrupt SpaceX. There's no money to be made from a Mars base. If it distracts from pursuing prospects that actually have economic demand, it will be a disadvantage that competitors will exploit.
SpaceX plows all its profits into this goal. (Its shareholders aren't getting any returns, not for a long time. The SpaceX investors are playing an extremely long game.) And if you constantly use all your profits to improve your capability, you have a huge long-term advantage over companies that exist to make a profit for their shareholders.
Falcon is not fully reusable, there's a hard cost floor from the need to throw away a second stage for every launch, and there's no reasonable prospect to avoid doing so. The idea is that Starship will beat Falcon on launch costs long term. SpaceX itself is chomping at the bit getting Starlink to launch on Starship instead of Falcon, because it will be cheaper.