Looking for Guidance/knowledge: why do ISP Routers struggle to maintain a LAN for Businesses?

I’ll try to keep this as short as possible:

I work in software, our company relies on iOS/android devices running our software to communicate over the LAN to external peripherals. Information is sent back and forth from device A to device B over the network and for whatever reason we have blacklisted nearly every ISP router, even ISP “business-grade” routers that we have ran into.

We generally push them to a specific router we have no issues with, my morbid curiosity wants to know why these ISP routers struggle with this though.

Are they just very cheap and poorly made? Why can these devices not maintain these connections over LAN?

Any nugget of knowledge would be greatly appreciated- thank you all!