Alot of forks are fairly basic so they’re home/shop servicable, when it comes to replacing parts you will need speciaist tools which cost and on the more modern forks you’ll get closed cartridge dampers that are far more involved and consequently easier to mess up.
The rear shock agin need specialist tools and seals to fully service so shops only do air can services which you can do at home.
Most of my mates that own/work in shops see suspension as too much of a pain in the bum to do as it can be messy needs alot of stock of parts and tools along with the margin on work isn’t great so are better off repairing and selling the bikes with suspension stuff coming to me.
The knowledge element is key, too knowing what does what and what is likely to fail and making parts to address design weaknesses, we still learn something everyday and only do suspension, I can do pretty muh everything else on the bikes and motorbikes if I want to but generally on more technical stuff it goes to a specialist.
Edit: the recons are really easy to do yourself, go on give it a go you’ll have to really try to break anything in them 😀