Because decision making, policy, leadership, management and administration is all that actually matters people's lives, whether they know it or not. Do you care more about the price of drugs putting your life in jeopardy, or whether the boss mis-speaks in an interview? To cite one of many examples. Biden has a very good track record on that front I've not seen anything to suggest it won't continue.
Important decisions are made carefully with all the analysis and relevant advisors around you. That's just how it works, important leadership roles anywhere, government or McDonalds, are about getting the right people around you and getting the best out of them. The common idiotic response is "well who's running the country!?" Lots of people, competent ones if you elect the right leader, but if people want a dictatorship, that's what they'll get.
And that was hardly a soft-ball interview, as one person said. Literally every single question for 25 minutes was about Biden's personal health and if he should step aside, every single one, ignoring anything said about his accomplishments. A Fox presenter would have been proud and they got their 10 second soundbite. It was a prime time showing where he did manage to list out his accomplishments to people who are perhaps on the fence and showed he can take tough questions without throwing a hissy fit.
Having said all that, 'image' is of course extremely important for electability, whether I like it or not, and his is on the floor. If a replacement has a better chance then he needs to go. That's up to the Dems to make the right call, hope its the right one because the whole world suffers this time if they don't win.