I had two friends who did about 1/3rd this distance at about the same pace. In an era before folding beads, if memory serves I think they changed their tires out before day one, carried lots of spare inner tubes, but ended up carrying spare tires figure-eighted long before they hit the Continental Divide. The roads in our county were exceptionally good. That alone made our organized events pretty popular, but the organizers were also really good at what they do.

Going across the country you're gonna be hitting way more counties and states than you would even as someone who travels for cycling events. More importantly you're also not on a curated ride. Our club was top twenty and people agonized over the relative safety of certain back roads. Pavement quality, debris, traffic, blindspots, pets. Sometimes they got it right, sometimes wrong. It was an iterative process and some segments were only ever tried once (or twice if people forgot why we said no before).

On a cross country trip you don't have locals curating for you, so it's going to be more wear and tear.