Although it seems like a large amount, there are many far wealthier 'whales' dropping larger amounts than OP. SO not sure why he/she felt the need to let us know the numbers.
Completely agree with you that what you described is the majority of the population, however Teens & young adults also make up a sizeable chunk where they either have a part time job/mommy & daddy with a cc, live off of benefits or F2P.
As for why someone would spend 500 euro a month online...Each to their own. Its a hobby. FOlks spend much more on alcohol, tickets for events, gambling etc. Also 500 euro is not that great. If it was £500 that would be diff. imo.