Because it doesn't cost much in either time or money!!
The test entry fee is now £600 (bargain)
2 hours flight time about £450.
I don't know what happens if you get a partial. Another £600 plus flight time?
Perhaps it's to discourage all those that aren't deadly serious about it, although money is an unfair way too differentiate?
It's certainly encouraging me to go for a first time pass!