What are the obstacles for using raft foundations?

in brief.
If design requirements doesn't show needs for raft foundation so it is uneconomical to use raft foundation as it will cost many times of other equivalent foundation.

it depend on the plan and distance from Neighbors and soil capacity and cost for project raft foundation it is necessary for higher building but for small building waste money

many factors type of soil geographic condition ,strata of soil and cost

It depends on parameters, but in general it is not advisable to use Raft foundation if we have few columns and bearing walls so we can go for separate or strip footing and make good saving in excavation and backfilling.

Raft Foundations cost a lot, actually in small buildings it is really waste of money, also it depend on the type of soil, raft foundations cant be used in any type of soil, soil must be tested, then you can choose what type of foundation to use.

Raft Foundations are very expensive.