XL was designed for GH4. Many users already had the XL and they bought the GH5, so you see the XL used more often. While XL accomplished its original mission and still did great with full frame lenses, GH5 had bigger coverage to begin with, having no 4k crop at all, and on top of that you need to give a little headroom for the IBIS to operate. You don't want an entire stripe of black to come up every now and then when you handhold (with XL and APS-C lens). If you don't want IBIS why didn't we stick with GH4? Everyone seems to be using the Sigma 18-35/1.8 and on GH5 an ULTRA is required. Of course XL if you use only full frame lenses.
