In-Game Parser.

[Felessan]

1. People wouldn't have figured out the perfect rotation without parsers to begin with.

A very good rotation can be obtained even without parsers at all purely on theorycraft basis of calculation of potencies etc, it's how most of work done before finetuning of minor details with parsers.

2. Isn't it a bit weird that we need to look up how to perform well on the internet instead of learning using an in game tool.

Most people are not capable of inventing a good rotation themselves, so they still will need some outside source for that.

But where's the fun in that?
I mean if we had an ingame tool like a parser, everyone could use that instead to learn how to perfom well.

You can't learn just by looking at numbers. You need to really look deep inside of your abilities and think deeply about a proper way to use them. You can do this part without parsers, just not many bother themselves. You can (if you know corresponding class) easily spot those 1-2-3 crowd that don't bother with maintaining debuffs and dots or have holes in rotation.