Although the costs aren't monumental, it does add up more than using basic hardware at home (I live in an area with fairly cheap electricity). I also work for one of the major cloud providers, so it kinda pains me to know how fat the margins are and how much I'm getting "ripped off".
However, whatever deal one may be able to cut there must be accounted for in terms of the rest of COGS, including salaries, taxes, and everything else. The company charges well above COGS in order to turn a sizable profit, and to give some room to compress the profit margin should another cloud provider decide to pressure them on prices.
Basically, the cost would be comparable if you invoiced yourself for your time setting up your homelab, and had to pay your spouse a fee for taking up a perfectly fine closet with noisy blinking lights.