Because they removed the write throttling to leverage the benefits of the new up to 128GB OS_DATA partition with a new VMFS-L filesystem instead of FAT. This overload the vmk_usb driver which the underlaying SD card hardware and ESXi becomes unresponsible over time and goes into a unmanagable stage. They made a fix for the vmk_usb in 7.u2x to get it back working including a statement short time after that in the next major Release of ESXi the SD/USB is not a valid install media anymore. BTW.  Since the Release of vSphere 7 it was never possible to order a Poweredge Server with ISDM and ESXi 7 preinstalled from factory! Regards,Joerg
Other than site always being a little slow and removing all my configuration after some kind of timeout with no warning, I'm also wondering about the VMware ESXi 7.0 selection. Seems I always run into a conflicting issue or two. It took me 15 minutes or so just to get the BOSS option to show up, needed to add the PCIe riser first but I'm not sure why ESXi 7.0 forces you to use the a BOSS controller card. Why can't I just use the ISDM Card Reader like VMware ESXi 6.7 can? 
PowerEdge R440 Config On Premier - Slow - Conflicting Hardware - ESXi 7 
Requires BOSS?