I really fail to understand or sympathize with Let's Encrypt limiting their certs so. What is gained by slamming the door on other applications than servers being able to get certs?

In this case I do think it makes sense for servers to accept certs even as marked by servers, since it's for a s2s use case. But this just feels like such an unnecessary clamping down. To have made certs finally plentiful, & available for use... Then to take that away? Bother!