Why are the Back End Developer projects focussed on Front End?

I only want to do the Back End Developer Certification, but looking at the projects, it seems to be heavy on Front End

Or do I need to wait for the API/Microservices certification to come out of Beta?

Can you give specific examples? Some projects are full stack (back end and front end), the majority of them aren’t, however.

for example the Voting app

Well, every back end project exists for the sole purpose of serving some front end. How polished that front end is is left for you to decide. It can have no CSS, for example.
The bulk of the obligatory work will be the back end.

we need to add authentication etc, or would we use the Clementine starter?

Not true, think about the heavy use of visualization libraries which are definately part of the front-end. The OP is right about the fact that the back-end curriculum is more of a full-stack curriculum, nevertheless, you are absolutely right about the fact that back-end and front-end should be learnt and dealt with the same respect.

I’ve been using passport.js for auth

You can have APIs as back end projects (that serve data for other programs), but that wouldn’t really be back-end as in “the back end companies look for”. That’d be API & microservices development.
Learning how to create a back end that will match a front end is extremely important, and what most people mean when they say “back end”. You can’t, for example, use all http methods because HTML isn’t able to use all of them, but in an API project you can, they are quite different in their approach and requirements.

Why not just build the back end / API of the full stack projects? That part is most fun for me too. Front end is a bear but I want to do full stack projects so I force myself to keep moving forward

Once you get past the API and microservices projects, I would suggest actually learning a front-end framework like Angular or React to do the rest of the full-stack projects. To me these projects seem more “full stack” than back-end, as you pointed out.