The fact that a card like Tarmogoyf goes for $200 shows that Modern is far from unpopular.
Modern isn't as popular because it's 1) expensive and 2) complicated. To play Modern and have any hope of winning you had better be ready to throw down chunks of $1K and know the mechanics of Magic really well (a good Modern player is probably more knowledgeable than most low-level Magic judges). You also have to know which cards out of the 10,000+ can be used against you. etc. That's a big investment of time and money.
Standard format -- $20 gets you into Sealed and Draft. $500 gets you the most expensive deck in Constructed. That's a LOT cheaper and you only have to know about a couple hundred cards.
If they really wanted Legacy or Modern to be popular, the solution is really easy. Put big prizes behind winning them. Suddenly everybody will be playing Modern.
They don't want Modern and Legacy to be driving things. They don't make money from those formats. They make money selling new cards--and that's all about Standard.