[nimbupani]

It is most likely because Opera was almost the only lone browser that refused to have 'Mozilla' in its user agent string from the very beginning.

A lot of websites still use UA detection scripts from late 90s(!) which STILL do antiquated UA sniffing which means Opera does not get scripts, styles or markup because it does not seem to have the 'Mozilla' in its UA string leading to broken pages.

There is an easy fix if it is an irritant which is to select 'Edit Site Preferences > Network' from the context menu on a page.

Also, we would be much obliged if you could submit a bug report if you come across a site that does not render correctly in Opera: https://bugs.opera.com/wizard/

If you are a web developer, please do consider using feature-detection :)