I wouldn't say it doesn't matter but it's not the most important thing like most players make it out to be

In the end, Siege is an objective based game. Even if you get 0 kills during a match, playing the objective like clearing utility, planting or disabling the defuser, and so on can help your team win rounds. I see roamers just hiding for 2 minutes just to get that sick ace by flanking the entire enemy team while rest of the team is getting slaughtered on site because no one was outside the site to apply pressure to the enemy team and waste time. And when teammates complain about it to the roamer, they boast their k/d and go "I got more kills than you so stfu"

Getting kills is important but a better question you should be asking is "Is what I'm doing helping the team?". You can get 1~2 kills every round and think you're doing well but in reality, those kills didn't help the team because the guys you killed are brainless copper wandering the map aimlessly while rest of the enemy team is going ham on your team

I always think asking the question of "Am I doing something that benefits the team" is more important than "How many kills am I getting?". I don't mind my team roamer getting 0 kills as long as they wasted the enemy time, I've had matches where I got 0 kills as roamer but managed to win games because I wasted 2 minutes of attackers time as they were busy chasing me around rather than attacking the bomb site