Even going by the low estimate number of 100k owners, at $15 usd price... that $1.5m USD.
With that kind of money on the table you really think they're going to waste time milking the 500 patrons?
Counterpoint, they've already made bank at 1.5m USD, the money they've made through multiple months of patreon income and the lowest estimate of 500USD per month remaining is just a nice little bonus. All they have to do is release a new update and people will probably resub or buy the game, rinse and repeat.
Granted, I do not think it's purely out of malice or greed, because as you said, they can make a lot more money if they were more consistent. I personally think it's either complacency, mismanagement, scope creep or sheer incompetence.
At least they need to have some transparency and communicate with the people that are subbed to them on patreon and their community in steam more frequently. You can't spend so much time without anything to show (that consumers can actually get their hands on, not just some gifs and pictures in a devlog) without garnering a fair amount of criticism. Hell, the supposed winter update from last year was delayed and halfway through 2024 they still haven't released anything.
The devs being lazy COULD be true, depending on how substantial the next update is (and it better be worth the year long wait but I doubt it), but they are absolutely milking patreons. Even if the amount is not that substantial, they are still taking in the money of people with absolutely nothing to show for their customers.