Semi Slav - Why do white players (top level) no longer play 5.Bg5

Hi forum members,

this is my first post in the forum.

I have been exclusively playing 1.e4 for the past 10 years and am now making an effort learning d4 openings. I am learning from an old book series from the early 2000's by Alexander Khalifman on 1.Nf3. Against the Semi-Slav It advocates playing 5.Bg5. However, looking in my database I see top players more or less exclusively playing 5.e3. I heard the Meran system is popular now adays and perhaps there is some new theory for black in the Meran System?

Thanks for your answers!

Thank you chesschess_historyphile.

Do you think it is the Camridge Springs Defence that has got new theory for black that is hard for white to find an answer to or is it more likely that it has been "analysed to exhaustion" as you say?

There are plenty of top level games being played with Bg5 in the semi-slav.