Because I can do it without any slowness.
I'm one of the two Opera users.
I've tried using all manner of sites like Pinboard, but none of them work as I like. I want a one-click bookmark button where I don't have to tag anything. Maybe I should finally get around to building the bookmarking app I really want.
Pinboard has several different bookmarklets you can use. One of them is a single-click one that tags the page as "read later".
With some one-click extension.
Reading up on one alternative often leads to multiple links which I can either read one an one, return from, figure out what is the next link, follow that, maybe recurse another level then step back etc. To me this is cumbersome.
Instead of keeping this tree in my head I can just ctrl-click any interesting link, ctrl-tab to the next tab when I'm finished with the current one and continue ctrl-clicking.
Finishing up I can even use the save tab set feature of pinboard to stash it all away under a nice label.
Personally, I find I never need more than ~10 for the task at hand. Also, if I ever DO have more than that open, the titles get too small to read and I start forgetting what I have. I either go flipping through all of them to find one, or I just give up and open a duplicate tab, making the problem worse.
Instead, if I want to look at something later, I usually tag it in Pinboard. Later, I can scroll down through a readable list of things I've recently bookmarked, or if I vaguely remember it, I can search by tags or text to find it.
Given this, I can't see a reason to have so many tabs open. Can you explain why you like to work that way?