Here's why:

- VTOVL works irrespective of vehicle structure. This means that you can have a highly efficient structure. In contrast, VTOHL requires either wings or a lifting body, either of which add significant mass and structural inefficiencies.

- For VTOVL vehicles which do a base-first re-entry, the dynamic loads are all on the same axis, once again leading to greater structural efficiencies. In contrast, a VTOHL vehicle experiences dynamic loads on two axis, once again requiring a heavier and more complicated structure.

- HL landing gear is very complicated, and needs to be quite heavy, compared to VL landing gear.

- VTOHL requires significant ground infrastructure -- long runways, and either launch towers at the landing sites, or a complicated ferry system. VTOVL requires a level concrete pad barely larger than the vehicle itself, and since it can stand on its own, no launch tower.

- VTOHL won't work on the Moon or Mars; VTOVL is what's required there. Might as well get experience with it now.

So basically, the only real drawback of VTOVL is that you have to carry extra landing fuel -- which is largely mitigated by all the VTOHL mass penalties described above -- and that your engines have to work reliably upon landing. Then again, everything has to work reliably for a HL vehicle as well -- since a HL vehicle generally isn't fueled, it must land dead-stick and get it right 100% of the time. VL vehicles are more forgiving in this sense, in that adding a bit of margin to increase the hover time is relatively painless, compared to giving HL vehicles a fly-around capability.