Currently there is DNS blocking (e.g. gambling sites in Poland), and it handles most cases. If (too many?) people start circumventing that, will a government start insisting on more invasive measure (e.g., DPI)?
The ISPs are not inclined to pay for DPI or whatever other nonsense, even if they believe it could be effective, which it probably can't be. Government does not want to take on a major budgetary extra to pay for something that's already unpopular. So that leaves it not getting done. Much hand-wringing.
The government already acknowledges that Tor completely defeats all existing attempts to censor the Network, but they supposed that DNS blocking is affordable and good enough. So, we make it no longer "good enough" and then too bad for their stupid policy.