I've never been big. I mean, I've gotten bigger at various times putting on weight but I've never been fat. That being said, the way I can put on muscle and retain fat without leaning out by lifting weights, leads me to believe if I was a man, I probably would have done well as a linebacker. LOL
But I agree with your sentiment. I've always leaned out super easily when doing cardio. Like when I used to be a runner. I also wasn't calorie counting then and still couldn't keep weight on. It's like the total opposite of how my body reacts to weight lifting.
During Covid when the gyms shut down, I was doing various forms of cardio & HIIT - running + dumbbell & resistance bands workout one day, long bike rides the next (which in SoCal, you have a lot of elevation variances so it's not like riding a bike in Houston where it's flat), hiking up the mountain, running steps at the convention center & biking back home. I was really skinny during covid but muscle was lacking. I also wasn't calorie counting then either & drinking a lot.
I just can't figure out why my body responds really well to cardio but not weights.