There are definitely airline seats where the reclining seats impact the knee room. I'm 6'2" but I seem to have more of it in the legs than typical, which really shows up in non-extended legroom airlines. I buy the upgrade whenever possible, but sometimes it's just not available.

In a regular (not extended) seat, I have two positions that work: my ankles crossed and tucked up close to my seat with knees spread, and nothing in the underseat in front of me and then putting my feet there, with my legs straightened (wedging my thighs into the edge of my seat). Even then, my knees are high enough that usually the person in front of me reclining will recline the seat back into my knees (best case) or those metal side rails into my knees. Especially enjoyable when the suddenly recline the seat.

Not everyones body geometry is the same. My son is around the same height as me, but when we sit in the car he's like half a head taller than me, he carries a lot of his height in his trunk where I carry it in my legs.

It feels like the same phenomenon when people bitched and moaned about having to take even the slightest COVID precautions.

In other words, you are inconsiderate.