Arms Deal came out in 2013 [0]. 1.6 came out in 2000, so that is 13 years (not considering CSS came out in 2004, and CS:GO was in 2012, without any monetization).
Fortnite is coming onto 8 years old now. The idea of it being around for 5 years longer is not particularly alien.
e: Actually, I should really be focusing on the time from Arms Deal to the present, which is 12 years. So, Fortnite has even less time to catch up to CS' current lifespan with gambling.
Most games that are that old, don't survive.