We all know that Intel always use a cheap TIM for their processor to encounter user from overclocked their processor due to Intel have capped the limits of their processor or really want to cut off operation budget.
Enthusiasts want more than rather buy expensive processor but stuck at the stock clocks speed and want to break the processor limits by OC and do some experiment which increase the efficiency of its, by remove Intel stock HIS enthusiasts can achieve more than capped stock clocks.
New Intel i9-9900K and i7-9700K CPUs are coming with gold soldered TIM/HIS to the CPU die. This should help manage the temperatures of the higher-clocked CPUs and will also help with achieving higher overclocked frequencies. Our Sky “C” super-laptops are ready for 9900K /9700K
Different matter with Intel core i5-9600K, that not confirmed to use TIM or paste but likely for that range of price it show TIM is a correct answer to use it as to secure that price and more focus to high end processors like core i7 or core i9.
Intel already shown us as they like to release high end processor first and make a good advertise to attract more people to buy, but for enthusiasts they want to enjoy overclocking more than use stock clock speed.