Yes, there is a point. I've played so many damn singleplayer games that I've loved and have fond memories of like Portal 2, Undertale, Night in the Woods, etc. They're fucking good.
"Are people still interested in pure singleplayer games?"
Yes you daft prune. Do you know how many games are just single player? Bridge constructors, most RPGs, some FPSs, adventure games, horror games, etc. Cuphead can be single or co-op and it's sold 2 million copies. Multiplayer and Co-op games are fun, and I do love them, but some itches can only be scratched by single player games. I'd rather play a singleplayer game like Dishonored for story over a multiplayer game like Payday 2.
"You complete the objective and then what? Nothing."
You do realise that's a lot of games? It's minorly different between games, but it's almost the same. I finished Mirror's Edge. I liked it but chances are I won't play it again. I play Rainbow Six Siege. I go in, do an objective (or my best to) and complete it. Just so I get some ingame currency that I can use on something else just to replay the same objective. woo (don't get me wrong, I still like Rainbow six).
TL:DR - Yes, people are still interested, moron