You are lying or not paying attention. Got to Tokyo and you’ll have plenty (as per Japanese standard) of trash in the streets specially near Shinjuku and Shibuya
And yes they mostly take their trash with them as there are no trash bins. But is it a smart design though?
I don’t need research because I’ve been to Tokyo plenty of times and I saw in fact lots of trash in the ground.
And again you’re wrong, trash bins for recycling do exist in Europe because I use them all the time, and I also happen to have visited lots of European countries and I didn’t see that much more trash in the ground than Japan. It’s true for cigar butts (its mind boggling in the Mediterranean countries) , but not trash. You probably had one “bad” experience and are using that evidence anecdotally. You are comparing Japan, a country, to Europe, a continent, it’s not fair