Many people use it as their "computer" nowadays. A smartphone is too small to browse certain sites, but a PC is not necessary.
I don't think the lack of multi user is important for most people, but it would be a really nice addition. If you have kids you want their iPad to have limits (something you can do with iOS 12) and don't have certain apps. But what if you want to use the device yourself? And even if the kids are grown up everyone has its Facebook account, mail, messages. You don't want to have every email account synchronised on the same device.
Maybe many people will share everything with their spouse and don't need two accounts, that's fine. But having the possibility to logout from the iPad and give it to someone else would be great. Of course every time you log in the system will have to open your apps from scratch, it could be a little slower, but I don't think you're suppose to switch between accounts every 5 minutes.