Maybe that's how much memory it takes to make it difficult for ordinary folks to use the phone on a carrier other than Visible.
I got one a few weeks ago too, just to check out how one goes about working around the carrier restrictions. It's actually quite easy to make it work on T-Mobile and AT&T. It also works on Verizon post paid without any tweaks. What I haven't managed to do, however, is make it work on another Verizon MVNO such as Xfinity Mobile.
I suspect it is just the phone using different classifications. My Moto E5 play system is 5.5gb vs your 2.2gb for example. My ZTE R2 even has 4gb of system. So 2.2gb is low and I suspect the rest is just shoved into other.
It's unlocked; it doesn't reject a non-Visible SIM. The issue is that the operating software is set on certain defaults that are locked out in a way that can't be changed by simply toggling through the settings. Specifically the phone is set on a default so that voice relies on VoLTE but the phone can only access VoLTE on Visible (and the Verizon mothership). Nevertheless, the phone has 3G GSM antennas. So you need a work around to change voice/text to 3G mode in a way that can be used by a GSM carrier.
The way you do that is to download an app from the play store that will force the phone to go into 3G mode for voice and text. The one that I use is Mobile Network Mode but there are others like it. Once that is downloaded, you change the toggle for "Set Preferred Network Type" to "GSM auto (PRL)" Voila. You have 3G voice/text access on AT&T or T-Mobile. Then, you just have to manually input the APN to get data.
Keep in mind that this phone is still not ideal on AT&T or T-Mobile because you are relying exclusively on LTE bands 2 and 4. You do not have bands 12, 17, 29, 30, 66, and 71. Your performance is going to be like using the unlocked Verizon version of the Galaxy S6 on a GSM carrier.