There's no pressure because the senators you named are locally popular.
The only people who care about this are massively online, pundit types who want a Senate full of Jon Ossoffs and Ayanna Pressleys for expressly partisan purposes. What Joe Schmoe in New Haven thinks about Richard Blumenthal running next year couldn't possibly be any more misaligned with the aspirations of the Twitterati, lol
Well this is just blatantly false.
First, there is the legitimate concern one of these fools could die. Leahy, who had a health emergency just weeks ago, is exhibit A of that.
Second, and I'm sure this doesn't matter to you because of your blue avatar but it does matter to rank and file Dems, underrepresentation is a serious problem and we've already seen that all things considered equal Dems are more likely to turn out for women, LGBTQ, and POC candidates, esp. when they belong to one of those groups. Whether or not you understand or appreciate why equity is important to the left, it is very important.
There's an offline constituency for it. "This guy isn't obviously flawed but he's old and out of touch and unrepresentative of the state and party as it is today." It isn't explicitly about their age and the idea that they might die in office, it's just what you see with lazy long-term incumbents in either party. The Dems just add the representational angle as well.
But when unless the incumbent is totally out of touch and inept, they'll usually win. Guys like Tom Carper, Steny Hoyer, etc. are out of the zeitgeist but they haven't gotten lazy.
