Well, your statement is not completely right… 2 more cores in gaming is useless for pretty much 99% of the games out there (in future games will be more optimised for multicore). When you compare the i9 11900k I guess you just watched few reviews online but they are not telling you the true story… there is a 12% increase in terms of performance depending on few configurations in the z590 chipset in combination with the new Intel architecture. Specifically, power limit can be removed (bypassing intel specs), set to intel specs or you can load the optimised one based on your matherboard manuifactor values and curves. Memory latency can be lowered down thanks to Gear mode 1 and XMP profiling (3200 Mghz are now natively supported and xmp 1 profile is stable with no overvoltage). Another feature of the i9 11900k is the new Intel Adaptive boost (based on the termal throttle, different cores are running at different speed and if there is enough room in tems of temperatures limit then they will run at higher frequency for a longer time). Finally you have the Extended Bar feature that could boost another bit although at this stage is not supported by many games. The most important factor is the cooling, the more you keep the i9 11900k cool the better it performs (see intel adaptive boosting and power limits).
That being said, for gaming, I need to admit the i9 11900k is not outperformed at all by the I9 10900k. I own both and Do I suggest to upgrade? NOT AT ALL!!! But I’d like to point out few things as I can compare the two products based on real world scenarios.