Very easy !!!
https://www.similarweb.com/fr/website/w ... tingx.com/ is the truth for various reason :
1 - it's the onlyone who correspond to data even if they are a bit under reality but it's normal.
2 - They are directly connected to google search tools and they are the only ones.
3 - They take in count the mobil and tabletts and apparently Alexa just start to do it now, but the are far behind.
For instance Pornhub is ranked n° 56 by Alexa and n° 10 by Similarweb. Easy to see the difference as you said. But because also now Alexa want people to pay to get statistic and they just fuck up all data.
When you see Alexa telling I get by biggest amount of viewers from Romania it's a pure joke.

- Alexa

- Similarweb
but SimilarWeb is right, Germany, USA, and France are my main clients in this moment.
And it's same bullshit about the forum :

- Alexa

- Similarweb
And the forum can easily show the stupidy of Alexa statitics, as we can all understand that most participant here are with english and french language first. Of course we have some indians but not as much as Russians ( n°1 visitors here ), American, German and French, Spanish, Hungarians, Czech, etc ... ( the forum is not locked in those two countries )
They are anyway under the truth about the traffic on the forum as it's between 25 and 30 000 People/day at this moment ( a bit less that in 2019 when I went to 35 000 /Day but it's nearly 800 000 month for the forum and actually 2,5 million month for WoodmanCastingX.
So I recommend you to watch Similarweb is you expect some serious informations.
PW