Jeff Findley wrote:

Seriously though, NASA has looked at horizontal landers before and they do
have several advantages. Visibility when landing, much lower center of
gravity (they aren't likely to tip over), and easier access to the surface
(no huge ladders for EVA or huge cranes needed to lower the payload to the
surface).

And, to be fair, one big disadvantage: clearance issues with staging
during abort from powered descent.