The operative word here is onshore, for a variety of reasons, like the absence of road/tunnel/bridge permits, neighborhood Karen councils and local politicians, having to manage multiple lease arrangements, etc, etc.
I read an industry article mid-COVID that claimed the biggest barrier to offshore right now was the lack of ships to install them - alleviated somewhat by the introduction of floating offshore rigs, like these:
So yeah, it's gotta be way cheaper to drop a couple of those in the ocean than truck towers out to middle-of-nowheresville or digging a foundation at the bottom of the ocean or whatever.