I can only speak for MIT, but its 5th year Masters of Engineering program does require a thesis[1]. It makes sense for a lot of students at MIT since many undergrads take graduate-level classes anyway (since they can also fulfill undergrad requirements and are often more interesting anyway) so it's only slightly more effort to do the thesis and get the Masters.

In my own personal experience, I was already done with the graduate class requirement after my 4th year, so I only had to concentrate on doing the thesis during the 5th year (though I also enrolled in a couple electives of my own choosing). For me, that year was relatively more chill than my previous years.

[1] https://www.eecs.mit.edu/academics/undergraduate-programs/me...

You get a lot of value out of a 4 year undergrad degree, much more than a masters. So just building on that degree immediately with more intense course work and some independent thesis project seems like a win to me. I would have loved to have had an extra year on my undergrad degree for some graduate-level courses and independent project time.