Why are YA users not able to comment on others posts anymore? ?

No specific reason was given. Some claim it was due to the rampant abuse (trolling). Others say it's because of the upcoming US election in the Fall. It may be a combination of multiple reasons. 

Yes, because of trolls like you.

It was a move against hate /slander talk.

Commenting on answers has been removed. For how long we don't know. It could be temporary, or it could be permanent.

Yahoo has Temporary Disabled Comments Until they turn them Back on you wont be able to Comment

on any Answers

They made a Announcement about it here is what they have to say about It

In order to strengthen and improve community and engagement with our audience, we are temporarily disabling comments. Our goal is always to create a safe, engaging place to connect over interests and passions. Please feedback to yahoocommentfeedback@verizonmedia.com

They were pointless. People just dumped on what someone said and it did nothing.

A lot of it has to do with no one is responding  to the comments as they may have their notification turned off, Plus they don't come back to reply to any of them and also too many of them will leave a nasty remark etc so they go rid of em. which is fine for me.

Verizon Media, NOT YA, disabled commenting on answers at 12:34 am EDT Thursday morning/Wednesday night for security and safety reasons. Commenting has been disabled across the ENTIRE Yahoo platform because of the steadily increasing threats and the possibility of massive security breaches. Yahoo did EXACTLY THE SAME THING FOR THE SAME REASONS in 2016 and 2012. Commenting WAS restored AFTER those USA elections. 

I know you are probably in the UK. What you may not realize or understand is Trump, the Trump administration AND a majority of the Senate have been trying to DESTROY representative democracy A AND THE INSTITUTIONS of the federal and now the state governments at an accelerating rate for more than 4 YEARS and counting. As far as I am concerned, Trump IS the Antichrist. I am NOT an evangelical or fundamentalist Christian.   

Notifications HAVE NOT BEEN TURNED OFF. 

Nobody knows, and if the suggestion-board is any indication, nobody likes it.

Why people post ten identical suggestions instead of voting on the most popular one is beyond me