Well yeah. Prototypes are not products, the last 10% takes 90% of the time, and so on.
Practically half the wisdom written about software in the last 20 years has been about the fact that just because you can make something that kinda looks like the thing at a glance very much does not mean you can make the thing. All those "small tweaks" you think you need to be finished usually turn out to require large redesigns, else you'll tank performance, stability, security, usability, or all four at once.
Meditate on the fact that people used to (and still do!) go to game jams and code games with freshly made assets in a day. I just did one myself without llms at the weekend. Whats the difference between that and making a game that people buy? Why does it take so much longer?