They use Let's Encrypt's free certificates from what I can tell; their certificates can be easily auto renewed and this is encouraged (which is one of the reasons their validity is short).
I am not well informed so i have no statement about it. But what I know is that there are different kind of
SSLs to serve different purpose. When you buy SSL from a service provider then they may not necessarily provide the auto renewal feature.
It's kind of how someone wants to run their service. Every single providers have their own choice.
I used to use HostGator for my hosting previously later I found out that they do not allow to modify the mod_security function. I tried to explain why It is important for me but they have their terms which I had to accept. On the other hand, I have to run my business too. So, I decided to move from them. I had to chose one who allows mod_security to modify.
In reality, most of the big service providers provide modification of mod_security but in this case hostgator had something different in mind.