The alternative offered was Kamala Harris. Thanks DNC.
First-past-the-post voting practically guarantees a two party system emerges over time: https://m.youtube.com/watch?v=s7tWHJfhiyo
The US gov has been worn way at for decades by unscrupulous people seeking power and made so unpleasant to work in that few young people want to go into political leadership - and those that do don’t get far enough to have impact (eg. Buttigieg).. hence, old ass presidents.
Truly impactful movers and shakers have easy access to capital in the US, can keep their companies and lives private, and achieve a very comfortable life. Why would anyone choose politics over that?
Finally, the US gov system of checks and balances was designed assuming it could be perfected incrementally, but long-lived systems also need cycles of renewal - think of a forest. That design flaw is showing up now as key systems are getting cracked open by opportunists.