Sometimes I hear about people just looking for "SSL certificates" because somebody told them that they should have one, and search engines would lead them to those websites; probably that's how it still works.
At work, we use a paid certificate that is good for a longer period of time (normally a year). So that's one benefit to paying, I suppose.
As far as encryption technologies and security, the traffic encrypted by a lets encrypt cert is just as secure as the traffic secured by a paid-for CA signed cert.
Let's Encrypt could have just as easily generated certificates good for a year or more. But the point of Let's Encrypt is to force you to do this in an automated way, using scripts like you suggest.
You're not getting around anything. The choice was by design.
(It's been a bit sinse I went through it but I think it may be as simple as a extra flag in the command to generate the inital cert)
