I have a 40B softie reef - the maintenance on it isn't all that bad. You have to plan ahead a bit more for water changes as SW needs to be mixed for a bit before adding it. With a good skimmer, the water changes are less than a lot of FW tanks. There is a reason I have soft corals and not the more difficult / demanding SPS or LPS corals. There is a lot more that goes into those - dosing and maintaining pristine water.
With SW, and reef tanks especially, the stocking level is also much different than FW. There are no schooling SW fish until you get to about a 6' plus tank, and even then there really are only anthias and they have specific feeding needs. So you've got a bunch of different species, and each needs its own space and territory, and that really limits the stocking more than the bioload. I've got a 40B with four fish right now (planning to add two more), the largest of which is 4".
That being said, the colors and personalities are different than FW. The 4 fish I have all have different behaviors, swimming patterns, habits, etc. I personally find that much more interesting than a bunch of tetras floating around.
SW is (typically) a bigger investment off the bat. But there are often good deals from people getting out of the hobby, so you can grab a whole setup for a steal. There are also a lot of ways to build for relatively cheap, but no matter what you do you cannot stock a good looking reef tank for cheap. I think what drives a lot of people out is having one large issue can wipe out the whole tank (disease, heater broke, power outage w/ no planning, dosed something majorly wrong, etc), and when you've got hundreds or thousands invested in the livestock it is disheartening emotionally and financially. This is why people with big systems also invest in backups, controllers, QT tanks, and the like.