Okies...
1 - nobody needs 45mp for Weddings. As most albums are 25x35cm or less even for a double-page spread 12mp is plenty. Around 20-24mp as most pro cameras are we already have more then enough to be able to crop hard if needed and give the highest printable quality images
2 - I shoot well over 90% of my Wedding images on a 35/85 combo and rarely crop much more than straightening, my 'crop' / 'zoom' is merely walking forwards or backwards. Anyone thinking they can just crop is stupidly lazy, but most still use zooms anyway, so that's 'cropping' already
3 - the D850 isn't as good at high ISO as its lesser pixel count siblings, in high ISO situations the 'advantage' of big crops would only show this more
4 - buying a pair, most Wedding togs use 2 of the same, is a waste of some £4000 over a pair of D750 (Nikon's best Wedding camera IMO), no pro would ever waste that sort of money as its not business sense
5 - even as raw compressed (lossless) files in my use they came in at around 60mp, 2-3x bigger than the D750, this needs MUCH more storage = cost, and slows down PP - the added time factor being the biggest PITA
These are just my top 5 but I'm sure there's others - so to repeat -
defo not for Wedding work
Dave