I am generally going to disagree with Albaby here.
(1) I think perception trumps reality and the media has done a good job setting the perception that both inflation and the border are Bidens fault and are a significant negative for YOU personally.

The question isn't why people believe inflation or the border are Biden's fault. It was why people think life was better under Trump.

Prices were lower and interest rates were lower pre-pandemic. People generally don't like high prices and high interest rates. So they believe that things were better under Trump.

Some of this is Biden's fault, BTW. His economic team very deliberately chose a path that would have much greater economic stimulation than the Obama-era recovery plan. They knew that there was a greater chance of higher inflation than with a smaller program, but they were determined not to repeat the "mistake" of the Obama recovery. So they went bigger, and followed it up with even more fiscal stimulus with the BIL and BBB issues. And even then, only got a portion of what they were trying to get.

Regardless of fault, voters preferred the pre-pandemic economy to the Biden economy. There are valid reasons for them to do so. Much of the difference between the two economies was due to factors outside of the Democrats' control - but that doesn't invalidate voters' preference for the pre-pandemic economy.