Why Sony mobiles are not as popular as Samsung and Apple mobiles?

As Sony is lacking in marketing, also there are few bugs that are very common in Sony Mobiles.

I think marketing may be one of the reasons.

I don't know about other countries but when it comes to India. 

Apple and Samsung invests a lot in Marketing-TV, Radio, Google Ads, Newspapers, Flyers, banners etc.,

If you don't create enough awareness of your product then the product wouldn't be popular.

I would say it's all about your choice. They are all good in there styles.