How long can blocks continue to gain weight before there is no more chance of higher stake?
I can only assume it's technically daunting for some to learn and use coin control. It's just easier to let them stake. I hope in the future we can build a wallet that's more user friendly.
According to the code, blocks will gain weight for up to 90 days. From there, the block keeps competing for stake with that weight. That's not to say your stake reward won't keep accumulating. Maybe someone else can verify this.