They actually do have more people to offer. The reason it comes down to these two is a special interest grapple that has come to control within each party.
It's obvious in the Republicans party, but I don't think people see it in the Democratic party or maybe they don't care. It's the latter for me, I don't care. Biden is a solid candidate, he's picked a solid cabinate and a did enough running mate in Harris. I don't care if he dies in office or falls into complete mental decline, politically speaking, as we have had those things happen before as a nation and it is not the end of the world when the 'ship' is being run right, with competent people.
We'll mourn as a nation and move on. As it should be.
I care very much if Trump suffers Narcissistic collapse or complete mental decline while in office for the same reason. We've all seen the sort of ship he runs now, as we have Biden. We don't know who is running mate will be this time, but we do know that ultimately it will be an incompetent sycophant. We dodged a bullet with Pence; imo I don't think enough people see how lucky we got that he actually did the right thing when his mettle was tested. As an evangelical Christian, making a hard moral choice might be part of his character in his own eyes, but the rest of us know and see how that is rarely in alignment with the right thing. After all, fascists love to make hard moral choices too, like who deserves to live and who needs to die for the good of the motherland. We saw how that turned out.
A second Trump term will be the end. I question whether there can be any future anyone would want to have if he takes office again.