Also you need a hundred million dollars to run a campaign at all.
Bernie snuggles up to the democrat party because even being extremely popular doesn't ensure you will be re-elected if you don't run a campaign.
The 2024 and 2020 elections cost $15 and $18 billion dollars. We literally spend more than it costs to build an aircraft carrier, for no reason. An entire industry exists to suck up that money every 2-4 years. All that money comes from rich "donors", who always want to ask how you feel about <X> before agreeing to give you that money instead of your competitor.
Most countries have strict limits on how much you can spend on campaigns, and limit how early you can start campaigning. Only in the US do you have to endure presidential campaign adverts in off years.
Only in the US have we decided it's wrong to prevent the rich from totally controlling our electoral process through their wealth and resources.
This no limits system means our politicians aren't even up for sale, they are up for auction. Can you outbid Dupont the next time regulation comes up for forever chemicals?