compared to high level players, we are low rated, but 1350-1400~ players are however stronger than a lot of online players (70~%)
Why do people say that 1400 is low-rated

It depends on your goals and the people you usually play against.
To someone like Kasparov or Carlsen, even most grandmasters are weak and not worth playing against.
But that doesn't mean everyone sucks
Anyone at 1300 has pretty much stopped putting e.g. a knight on an undefended square where the opponent can capture it for free.
Typical 1400s have been playing at least a year, and have a fair amount of knowledge and experience vs newer players. They can't be beat by making random moves and waiting for a big mistake and they'll basically never lose vs a new player.

WOOOW 1400+
That's high-rated for me and a lot of other players!
Keep up your practice and you'll get 2000+

When considered by percentile it isn't a low rating, but when considered against serious chess players (and by 'serious' I don't even mean those who spend hours a day studying it, I just mean those who play regularly) it is low.
I'm in the 95% percentile in most time controls, but I'm at best a fairly good chess player. Maybe a 'good' chess player, but only if we allow for plenty of levels above 'good', like 'very good', 'very very good', 'exceptionally good', 'first class', etc etc.
Chess.com is full of people who play one game, lose it and never come back or others who are happy to just keep coming back, playing games without ever learning anything and just maintaining the same level. They don't keep losing, even if they are rated 600, because they just get paired against other people of the same rating so they win some, they lose some, they have fun. They just never get any better than pushing pieces around.
It doesn't really matter what label people give to your rating though. I just play chess casually so I know that while my rating in some forms of chess may sometimes bump over 1800, I'm not really getting any better, it's just variance. Compared to people who compete in open tournaments I am low rated. Compared to chess.com average I am very high rated.
1400 is high rated compared to chess.com. If that is your playground then yes, it is high rated. If you consider yourself only in the context of more serious chess players then it probably isn't because only players rated below you would drop out of the reckoning then, none or almost none above you.

A few months ago, I was in top 100 for my age in US but quickly fell out due to blunders and more blunders. 1400 otb is a very strong social player, and didn’t get to experience it much since I pretty much leapfrogged class C in a few months. It is definitely not a novice rating. By 1500 it’s much more competitive. Had to book up on opening theory to get well into the 1600s.

Ratings and percentiles online don't matter as much as you might think. Just a few reasons include:
People that open an account, win or lose a few games, and never log in again.
People that win a few games when glicko is giving them hundreds of points per win, get up to 2000, and never play rated games again
Of course, 1200 can beat 2000 and get 2000 rating! or 1200 can beat 1400, 1600, 1800 three times in a row and can get 2000 rating.
But rating calculator says, the chance is only "1%".( It means, 2000 rated player will beat 1200 in 99 out of 100 games) If you think it is common, show examples, or try yourself.
Conclusion, you are talking about 1% of statistical fluke, rather than the reality.

WOOOW 1400+
That's high-rated for me and a lot of other players!
Keep up your practice and you'll get 2000+
Thanks

No, they are close to master level

What??
A lot of titled player here are around 2000, some point more, some point less....
A 2000 player is better than 99% of the players
I'm 1400 and I'm 83rd percentile. How is that low-rated?