I have to disagree with @ConorMancone for once. There are reasons, although bad ones.
For example, you might have hardware that is externally reachable and thus needs a public certificate, but getting that certificate onto the machine is a huge Pain in the Ass. As such, having a cert that you need to renew 4 times a year may be less desireable than a certificate that is valid for, say 5 years.
Furthermore, you may be a non-tech business and your hosting provider may offer you a paid certificate for X moneys per year, whereas you'd have to do Let's Encrypt yourself. It may be less money to…