Very good question.
I think there are three reasons:
1. Hybrid Systems lead to some land value capture – lessening political pressure.
Im thinking in particular of the system used in much of continental Europe where local authorities are able to buy land at existing use value, subdivide and profit from uplift. Its still a change on uplift but not full LVT. Also consider places like China and Singapore where development land is essentially state owned.
2. Full LVT requires advanced cadastral and zoning systems to work well.
In the UK for example which does not operate a Torrens system it is often unclear who own land and what the charges are on land. Also in Britian tax assessors would have to guess the tax aliability on land or operate the second best (though still workable) approach of only taxing land where consent or rezoning for an uplift is granted.
3. Until recently Politician relied on rising Housing Real Estate Values as a vital Political Constituency.
From the early 20th century on their was symbiosis between rapidly expanding cities aided by changes to transport technology, a rising middle class and a low dependency ratio facilitating purchase of real estate and credit. Housebuilding however could not keep up once cities reached a certain size and house prices rose faster than inflation. The bubble of course would pop but it pops so infrequently that like Japanese Tsunamis it becomes something of folk memory to never forget the risk. Until recently the size of this aging property owning cohort made them the dominant constituency politicans sought to favour – one that would be harmed by vanilla LVT. This of course has no changed and we are in a lag period before it is claimed by mainstream political groups.
In a sense the period of 20th century car based deurbanisation – following Henry Georges period – took the pressure off – but now can be seen as historically transitory.