I suspect that the real reason is that THS is saving some money by not sending out so many images of listings.
Yes, yet another deterioration for sitters.
I have switched off those emails, they are utterly useless now. Instead, I do my Saved searches from the web interface. Yes, clunkier, one needs to change the sorting order to get the newest ones first, every time! The workaround there is to keep that tab open.