yeah different perspectives and intentions, your argument is true, if a gambler is just aiming to have some fun using their spare money they are just going to deposit and they will not mind about any deposit bonuses, while for those who are regular and heavy gamers they will take advantages of casino offers regarding to VIP's.
They will aim for that to achieve those additional perks that the house is offering and make a good use of it while using the house platform/services.
I am a regular gambler, my goal is really having fun and getting the excitement when placing (small) bets. I always look when a site offers a deposit bonus, but most of the times the requirements are pretty high and than I let it pass by. Their are some exceptions as they are sites that have a different system to unlock the bonus and than it becomes interesting.
Bonuses are mostly for those who are heavy gamblers, like betting a lot, because most of the bonuses for existing gamblers are rare and there are requirements to reach, like bet with 0.1 BTC to qualify. That is why most bonuses are only for new users, as it is their marketing to attract customers. Though mostly raffles are implemented so that old customers can join and have a chance to win huge if they get lucky, again, it is for marketing purposes. Gambling is a business, so they still need to earn profit before giving it back to their customers.