The people selling the systems often don't fully know the downsides themselves either and in a sense they're incentivized to not know as it makes it easier to sell the lie that there are no drawbacks to having your HVAC system exposed to the wider web. But you are also overestimating the average skill of an IT person in these environments and the capacity for their IT or MSP team to step back and evaluate the security of all the systems they have to manage. There's only the ability to evaluate convenience vs security if you actually have the time to formulate the question - if you're drowning in ticket submissions you will likely fail to properly catch every such issue. Certainly for these larger EU corps they should have the capacity to make those determinations, but who knows exactly how the management of these systems were delegated. My bet would be it was the responsibility of an under-resourced team with too much to do already.
I'm catching issues as I can as the head of IT at an org replacing our Danfoss systems with something else, but it wasn't until about 1.5 years since the initial decision to replace them that I'm finding out from a sub-contractor of the contractor that there's a cloud app our HVAC network will need to talk to - which is not-so-funnily enough a requirement by the state for us to receive associated grant funding for a portion of the new system cost. This was never mentioned to me at all as the head of IT. It's not even a convenience vs security issue, it's a misaligned corporate communications and approval channels issue. In other words, the capacity to secure your technical systems is downstream of political organization.