I just took a couple months off of commuting after tearing a calf muscle. (mighty hard to pedal when that happens.) drove to work or took the train most days, leaving me to watch the cyclists instead of pedaling alongside y'all. noticed a couple of things while I was away:

Drivers suck. I was appalled at the number of times motorists cut close or simply blocked cyclists. News to no one, but it seemed much more frequent and egregious when I saw it happen to others.

Cyclists appear reckless. It seems like most cyclists run red lights and stop signs. As a cyclist myself, I could tell that most of them were slowing down and looking both ways before proceeding, which I confess to doing myself. But as a driver, even as one who loves to commute by bike, I found this infuriating. Mostly I think the problem was "cars aren't running red lights; why are bikes?" though there was also the petty resentment of losing ground on others.

Cyclists move at highly variable speeds. This may seem obvious, but compared to cars there is a lot of heterogeneity in how fast cyclists ride. Sure, there is the occasional leadfoot or slowpoke, but for the most part drivers keep up with each other. We cyclists are all over the map. Many of us are happy to plod along at 7-8 mph, while others are looking to maintain 13-15. And of course you have the occasional crazee trying to set Strava records downtown. Because there are rarely two bike lanes side by side, this leads to a lot of us darting into traffic to pass. It hadn't really occurred to me until I was watching from the minivan.

Lastly, I was a lot happier when I started commuting again!