I think this is due to government regulations and the restrictions that have been imposed in the US. In the US, new users can only withdraw up to $2,000 within 24 hours from ATMs, and some other regulations have discouraged many people from using Bitcoin ATMs.
That can't be the only reason. That's if there is a decline in the use of Bitcoin ATM machines. If you are to make use of your ATM card and you reach your limit, the Bitcoin ATM machine always has a slot for cash deposits, which you can use directly to buy Bitcoin. I don't think there will be a limit to how much cash you can deposit directly into the ATM using it to acquire Bitcoin. If the ATM card limit was the only problem, people could have sought to use alternative options just to access the machine, but there is more to it.