@balloonfu-sen@yarn.girlonthemoon.xyz many reasons, all of which make sense. Same reason why automobiles today do not have an inner tube either. Now, about bicycles:

Tubeless bicycle tires drastically reduce punctures because internal liquid sealant instantly plugs small holes while you ride. Eliminating the inner tube also removes the risk of “pinch flats,” allowing you to safely run much lower tire pressures. This lower pressure provides superior traction and a noticeably smoother ride on rough surfaces. Finally, without an inner tube rubbing against the tire casing, rolling resistance drops, making your pedaling more efficient.

Bottom line, smoother ride, better traction, less flats.