That’s correct: I use FOSS where possible, and if I must use closed source it must store data in an open standard.
As you insist on evidence: I can create and open 100% of my archives in all systems I use now or in the foreseeable future without installing additional software. RAR fails that test.
The other reason: RAR is a closed format, and like I said there are better alternatives that are not proprietary.
Likewise your philosophy is that RAR is best and you are free to have that opinion also without providing evidence.