Incursions, just like virtually every other PVE activity is calculated to have a ~limited ISK per hour… whether it’s mining, carrier ratting, missions, or incursions…
All of the above have entry-level amounts and also all of the above have bitter-vet amounts. The bitter vet amounts are not really exponentially higher per hour, yet are still noticable.
HOWEVER the bitter-vet ISK per hour requires higher end ships, higher end mods, higher end implants, higher end skills. ALL of which amount to 5-10 Billion ISK, depending on the PVE trade.
You can easily lose a ship in an incursion. You can easily lose a carrier to rats and your Rorq to rats, blops or by not paying attention to local. It takes a LONG time to replace any of those, even entry-level ships/mods.
You should expect reward for large amounts of investment, both ISK and time especially. I admire those who can carrier rat for 8-10 hours. I start crying after about 2 hours and asking if Eve is really worth it.
Bottom line though, if you put in the time and effort, you should be rewarded for it, otherwise what is the point of playing a game at all?