Probably because of lack of $$$$$$$$$.
Actually, in relation to other studies, DNA and radiocarbon dating are not that expensive.
I am sure that any good research lab would sequence the Hobbit teeth for joint publication rights. If it had to be paid, the last sample of old bone I sent to a commercial lab was $1,500.
AMS radiocarbon dating of a tooth at one of the largest commercial labs would be under $700, counting the bone surcharge.
In terms of the interest and information potential, cost is not the problem. There must be some other reason a few of those gorgeous teeth have not been sent off for testing.