I think smartphones don't have recycle bins, because on the computer (for me at least) all files remain in the bin forever until I decide to completely empty the bin. Until then, my files aren't truly gone and they still take up a lot of space on my HDD memory. And smartphones don't usually have a lot of memory. Removing an app or file to a recycle won't clean your phone's memory space, it would just mark a file for deletion later.
Writing it down, I just thought of why a PC has a recycle bin: There's HDD memory for data, and SSD memory for apps. SSD is usually smaller, so when you don't need an app or big game anymore, you delete it and everything gets moved from SSD to the recycle bin on HDD, where you can still delete it completely or restore it later. Just a thought, there might be more to this.