Only one had the eSata port [DS218+] so is understandable why it was removed bbbbbut to also remove the 2nd USB port on the back is plain mean.
The DS720+ lost a USB port on the back. So this seems to be some trend to limit use of USB devices. I remember hearing that support in DSM for many USB peripherals has been [or will be] deprecated but external HD and UPS are pretty fundamental add-ons.
I mentioned this when DS220+ was first, almost, announced.
Plus = Intel CPU and RAM slot. Or so Synology's thinking seems to me.
The DS220+ should've moved to the DS7xx+ case, like the DS418play/DS420+ has the DS9xx+ case design. This would have allowed the DS220+ to accommodate M.2 slots ... which seems to be a mandatory 'plus' feature except in the 2-bay.