then why some ppl really custom all the way ah? it's the board that is ex or ?
Customs are usually for the following reasons:
1. Range of options for the switches; other than Cherry, there's options like Outemus, Gateron, Kailh, along with the boutique stuff like Zealios, Input Club, Novelkeys and many others.
2. Programmability - don't know much if production boards these days include this feature, but one of the nice things about DIY in the past was that you could customise your keymaps and also key layers for different purposes (e.g. for photoshop, gaming etc).
3. Specific cases, and maybe specialty plate mounting design - Usually all metal, could be small-shop machined and anodised for the really high end stuff. Some cases tout gasket mounting of the plate (over regular screw mounting) as a premium feature.
1 and 2 usually is available in even in entry level DIY.
3 is usually where the big money goes, for the keyboard itself.
Keycaps is the other black hole for wallets, but kinda unrelated since it's mostly aesthetic related once you get past a certain quality threshold.
Edit: Also, to add that even for entry level DIY, if properly set up (with sound dampening foams, lubed switches, modded stabilisers), can feel much more 'quality' than off the shelf boards.
I'm actually not a big fan of hotswaps. It's good for a tester board for trying different switches, longevity will be an issue down the road. If you don't intend to be pulling out switches and switching new ones in regularly, no reason not to solder it in instead.