To say Elementalist isn't good in the game because you don't see it as much doesn't hold any merit.
The screenshot, labeled as 12.05.2021, isn't useful. There will be an absurd amount of necromancers. Why? Well they just got a patch for their condi side, yesterday. You are going to see a major increase in necromancer population until all the testing, hype, etc, dies down. You may as well say all other classes, other than necromancer, are useless, as well, because I see 7 guardians.
I main a necromancer and play an elementalist. What I choose to do depends on the content. It is easier to carry bad/pug groups or do solo content on a necromancer, than it is an elementalist. Necromancers can be tanky, with okay-ish damage, and good survivability compared to an elementalist that is more glass cannon with less self-sustaining tools, but high-end damage. If I am speed running or doing set groups, with people I trust, I run elementalist.
Next thing you would need to look at is, yes, there are a lot of necromancers running, most likely for practice/test purposes, but how many of those groups were actually successful, and even, within a decent time period? Unfortunately that is data you can't really see, unless you are there. These are pug group scenarios, which is where a necromancer will most likely thrive. In a preset group, with good/better players, elementalist will be far better in comparison.
I would like you to watch to see if the meta actually shifts any within a month or two, not the day of a patch. Data needs to be collected, information pulled, scenarios tested, and it doesn't happen in an hour. See if people are actually wanting a necromancer for any sort of benchmarking. When the hype dies down, the class populations will spread out again.