Because that cannot continue in perpetuity. The cracks are already starting to show. If I were in my 60s faced with the real possibility of living another 15-30 years I'd want the younger people to feel like they had something to look forward to. Many young and middle-aged people in the US don't feel that way. What they can't get through the ballot box, they'll get other ways, ways that will cause others to say "I'm not saying I agree, I'm saying I understand."
It's the job of government to make sure that doesn't happen, not cater to it.
They're not thinking that far ahead. Their response to the first waves of discontent - Occupy Wall Street, Trayvon Martin Protests, Michael Brown Protests, Charlottesville, Freddie Gray Protests, George Floyd Protests, January 6th - was either to mock or chide the aggrieved, or to cast them as unprecedented threats to the nation's security (but then not actually do anything to address grievances or even punish transgressions). So much stuff has burned in the past 1.5 decades, there's still not a wealth-adjusted plurality of Boomers who want to fix anything. Their tacit rallying cry came from Biden: "Nothing fundamentally will change."