Trump, Biden, and Bernie are all too old. They could all die at any time, and thus it’s not an effective political argument for either side.
The reason why Biden is being attacked from that angle more effectively is because he is showing signs of dementia. That’s a whole other issue aside from the likelihood of death.
To be fair, the men’s rights movement is absolutely characterized as alt-right by the mainstream media. People tend to assume all sorts of things about you when you bring up any kind of men’s issue. Most people (including other men) have difficulty empathizing with grown men, and thus they subconsciously expect that men’s advocates are motivated by something else, such as misogyny. It’s hard to move past our biological and cultural tendencies and view men as vulnerable and in need of support.
Don’t hate the player, hate the game.