Front-loaded machines with both a washer and heat-pump dryer exists. I've had one for many years. It's quite handy if you have light loads, but I much prefer having a stack of separate washer and dryer, even though it means I have to manually move them from one to the other.

You know I had the vague thought of searching to see if they were actually out there but dismissed it as unlikely (at least in NA) because I've recently been appliance shopping and never saw one in person.

Combo washer/driers exist. They typically have less capacity than stand-alone units.

Drying performance is shit. Especially since you can pack a washing-machine fairly full without affecting performance, but a tumble-dryer needs to be loosely filled. But even so, the combo machines don't dry well.

Probably because that would much more mechanically complex and therefore expensive and failure-prone, and the market has decided that the existing options are good enough (I'm not defending this, just describing what I see).