The simple fact that there is no Bitcoins left for selling. Everybody is holding them waiting for $100+k. The 21m supply of Bitcoins is not enough for the all companies, individuals and governments interested in Bitcoin.
It seems that corporate investment drives this bull run, as prominent investors, like Raoul Pal and Michael Saylor invested half a billion each in Bitcoin and are almost double already. Their competitor fund managers and investment companies now want to follow their example.

However, the general public is still not aware of what is happening with Bitcoin. They'll probably rush when a new all time high is reached