Most likely the main reason Obama is staying quiet, beyond knowing his efforts would backfire, is because of Biden's frailty. At this point I don't really think Pete and Amy dropping out would even necessarily help Biden - he should, by all measures, be pulling away from Pete (Amy, other than New Hampshire and press hype, has mostly been a nonstarter), especially with the move to more diverse states, yet they were still relatively close in Nevada.
If Steyer's results in Nevada are any indication, then polling may be vastly overstating his support. So that would be good for Biden in South Carolina, but when people seem to be seeking out so many alternatives to Biden, then it suggests he just hasn't managed to win their support, and I'm not sure he would even if everyone dropped out and endorsed him.
I don't really believe most of the people running genuinely care about anything beyond entitlement and/or grifting. I think that
Biden and Warren are the main exceptions, which is why I'm sad to see where they've ended up.