Is there a lot of demand for timestamping? Are people willing to pay for it?
There are already free, centralized services that will timestamp arbitrary hashes for you. Besides the risk that they might go away (which you could mitigate by getting timstamps from several of them), is there any real advantage to using the blockchain?
If I can already get timestamps for free, why would I bother to pay a transaction fee to get a blockchain timestamp?
I'm often wrong, so feel free to ignore me, but blockchain timestamping seems to me like one of those gee-whiz ideas that appeals to us techies but isn't "enough better" than existing solutions to be interesting to non-techies.