A few years back the founders got removed and there was a shift to quarterly profit and they stopped developing and maintaining their own rendering engine and browser to basically become a skin for google chrome, saving costs. In the recent times they improved their skin status and tried to sell the whole package and managed to do last summer to a chinese consortium of investors.
I suppose right now opera gets its money from the deep pockets of rich chinese investors, the current business model might have something to do with surveillance capitalism.
And I do use Opera as a default browser.
The correct Ctrl+Tab behaviour which works like Alt+Tab (switch between the most recent tabs, with a small popup list of tabs) is the main reason for that. Much more productive for me than the usual "cycle over all of open tabs sequentially" behaviour that Chrome, Firefox, and everyone else have (except the Vivaldi browser).
[1]: https://addons.mozilla.org/en-US/firefox/addon/tab-mix-plus/
1. Go to about:config
2. Search for browser.ctrlTab.previews
3. Change value to `true`
4. Close tab
Now your ctrl+tab should work as you want.
If you wanted multiple sites open you had multiple browser windows on the taskbar.
That became unmanageable quite fast, so we got tabs.
Note btw that even the earliest Opera had "tabs". It used MDI to provide multiple sites within a single browser window. This stuck with Opera all the way to version 12. After that they changed over to being a Chrome clone.