Because others are jumping on the mirrorless bandwagon and becoming fanboys?
Unless you desperately need some feature which m'less offers there's no point switching. And look into the disadvantages the fanboys gloss over too. One person's game-changing feature is another's irrelevance.
I actually agree with the sentiment of that even though I have switched over completely too mirrorless.
For an amateur photographer that is just taking photos for their own enjoyment, if they already have a decent dslr set up there isn't going to be a night and day advantage.
For a working photographer those small advantages can add up to be too be a huge advantage though, although possibly not for everyone.
As a wedding photographer there are some things on the mirrorless systems that just make work easier and faster and that for me was well worth investing in.
E.V.F - being able to see what you get is a huge bonus, that shouldn't be underestimated. It has made a huge difference for me and allows for more creativity.
100% reliable A.F - This of course is a huge difference, I can have complete faith that if something isn't right it is my fault not the equipment. This has allowed me to deliver more images to clients. I am sure any wedding photographer that has used a dslr will agree that at every wedding there is a decision to make on at least a few images that are slightly out of focus, in terms of if they should be provided to the client or not. That's no longer an issue, the a.f performance is now so good.
Not having to tune lenses - For an amateur photographer this may not be a big issue. However when you have a large amount of glass it's a pain staking annoying process that takes up time and is frustrating. Over time focus shifts as well so it's something that needs to be constantly kept on top of. When I shot dslr's I felt I had to retune all of my lenses every 2-3 months to keep on top of it. This was especially annoying when buying a new lens and over the years I returned many lenses that where too far out to tune correctly. Just as one example I had 5 copies of the Sigma 50mm Art that had to be returned for front and back focus issues.
Lighter weight - Yes, the weight savings aren't huge you can't beat physics and high end glass will be generally as heavy on mirrorless systems. However there are some very high quality light weight lenses around like the Sony 24mm f/1.4 G.M (the lightest 24mm f/1.4 available from any manufacturer) The bodies are lighter weight than the pro dslr bodies. Those small difference on a 10-12 hour wedding day, make a huge difference. Before I switched to mirrorless I would come home from a wedding absolutely exhausted and would often just dump everything and head straight for bed. The next day I would still be knackered. Not any more.
Quality of the lenses - The high end mirrorless lenses are pretty spectacular, add all the in camera corrections on mirrorless bodies and they are a treat to use. Newer equipment is always improving. When I shot dslr's I absolutely loved the Nikon 85mm f/1.4, the Sony 85mm f/1.4 G.M is a much better lens and I much prefer its rendering as you would expect as the Nikon lens is a much older design.
Silent shooting - When I shot dslr's there where often moments that I felt like I was intruding due to the shutter noise. I still took the photos but it made me feel uncomfortable.
Software improvements - The manufacturers seem to find it easier to provide software updates on mirrorless gear that make a difference than they did with dslr's. I can't really think of any software update that Nikon ever provided for my dslr's that made any real difference. These where generally just to fix issues. Sony have added animal eye a.f via a firmware update, improved the already great a.f system on the A9 and who knows what will come next.
Those are the main advantages for me but if I was just shooting stuff for myself I would have been just as happy using the Nikon D750's I moved away from and probably wouldn't have considered changing until I had too.
If I was an amateur photographer and starting from scratch I wouldn't bother with full frame any more and would pick up an A6400, which is a superb little camera and a few prime lenses like the Sigma 30mm f/1.4.
