You have to zoom out a bit. EVs are still improving of course because they are relatively new. It's not fair to compare that to the last few decades of car history. You can make any flat looking graph look steep by zooming.
EVs are as old as ICE vehicles, people should compare both on the same scale.
The only part of an electric car that hasn't been in development for at least as long as any ICE vehicle is the battery. So really it all comes down to that one thing.