When I went to uni a few years ago now, all the lectures were recorded and put online anyway so most of people didn't even turn up. You could call it laziness, but it was honestly more effective to watch an online lecture and be able to rewind, pause to google something, watch at faster/slower speeds etc. Obviously we still had regular in-person seminars and interactive tutorials, which I imagine Manchester uni will also be doing (hence why it's 'blended'). Ultimately, I think the best reason to have lectures online is the massive benefit it has to students with disabilities, both physical disabilities and things such as dyslexia.
Maybe I'm just miserable, but I do dislike the argument that lectures must be in-person so students don't miss out on socialising and the "experience"... university is a place for learning and contributing to research, not for socialising. A student's desire to socialise at a lecture does not trump a disabled students desire to learn effectively.
Also, as mentioned, when I was at uni attendance at lectures was very low anyway due to the recordings (which I understood to be the norm across the whole uni, not just my course), we still had a very active social life with people on our course due to the seminars, tutorials, and most importantly the events and parties 