i guess one of the reasons they're doing is because the concept of fashion shows is super expensive and dated. everything happens on social media nowadays.
This is a very old issue indeed, it reminds me of the famous quote attributed to Churchill on democracy: it's the worst form of government, except all the others.
Every now and then, designers try to break the mould, then they go back to the good old catwalk (Rifat Ozbek is the first I can think of, with his SS90 collection shown on CD, then others come to mind: Romeo Gigli, Helmut Lang, Gareth Pugh...). There must be a reason why digital only does not really work (which I think has mainly to do with the fact the clothes are physical objects and their features cannot be fully communicated via film).
Plus, I would add, doing catwalks would not exclude other more experimental ways to show your work - wouldn't it be great, for example, if resort and pre-collections of sort, instead of the lavish (sometimes tacky) extravaganzas at the four corners of the world we got used to, were shown digital only? IG works to peddle products - which ultimately is all CEO's care about these days -but when it comes to real Fashion, catwalk seems irreplaceable: could we imagine the work of Galliano or McQueen without the shows? Even the brisk affairs that HL used to call "seances de travail" were integral to his message.
Of course, these are top creatives that we are talking about, the same could not be valid for Virgil or his various clones, but still...
One last thought: shows can be expensive but can also not be, depending on whether you use them as a tool for professionals or a marketing stunt. And I guess paying a crowd of influencers does not come cheap either - at which point I'd rather keep the crappiest show rather than seeing another IG selfie from a nobody preening about.