That's because no president has committed any supposed crime of any importance.
Nixon probably did, but resigned anyway, and was then pardoned, so it doesn't really matter.
Clinton was a technicality, and never removed from office, and no one cares really. Lewinsky is a celebrity now.
Trump... well the first one was obviously political (many Presidents deny foreign aid, etc... it's part of foreign policy. Biden is famously on tape as admitting to doing the exact same thing) and the second one was on thin ice as Trump explicitly called for peace
"Using the powers of his high office, President Trump solicited the interference of a foreign government, Ukraine, in the 2020 United States Presidential election. He did so through a scheme or course of conduct that included soliciting the Government of Ukraine to publicly announce investigations that would benefit his reelection, harm the election prospects of a political opponent, and influence the 2020 United States Presidential election to his advantage. President Trump also sought to pressure the Government of Ukraine to take these steps by conditioning official United States Government acts of significant value to Ukraine on its public announcement of the investigations."
Like it or not, the allegations against Biden and his son have only become more substantiated over time.
Trump should not be punished for investigating.