While I don't think that 4e was designed specifically to sell miniatures, it's pretty clear that they still had that in mind to try and monetize the brand. While they list miniatures and battlegrid as only useful in the player handbook, they do list them as necessary in the Dungeonmaster Guide, also proposing their Dungeon tiles and Dungeon Miniatures line of products of course.
But they did eventually offer an alternative, at least when they launched the Essentials line, with Monster Tokens coming with the Monster Vault. So I don't think they were malicious about it, I think they just wanted to make combats as tactical as possible, and the best way to do it is with miniatures and a grid, or on a VTT. And well, they're a buisness, so of course they'll try to sell their product and find new ways to use them.
The problem I think is not that they tried to monetize the brand by 'forcing' players to buy miniatures, it's that they expected that every DnD players wanted more tactical combats and they made their rules accordingly. They didn't take into account that a lot of players prefer to play Theater of the Mind, and well, while I know that it's possible to play 4e without any miniatures (I do it sometimes when I don't want to bother making a map), it is much better played on a tactical grid... If someone wants to play DnD without miniatures, even if 4e is my favorite edition, I would suggest playing another one.
Let's not forget that, compared to pretty much every other hobby, TTRPG is pretty cheap... you usually just need one or two books, a couple of dice, pen and papers and you're all set. And more often than not, it will be just one of the players buying the books, not even considering the fact that books are pretty easy to pirate on the internet. Compare that to CCG like Magic or miniature game like Warhammer and as a business, it is much harder to monetize the TTRPG. Since WotC were selling the DnD Miniatures game back then, I think it is only natural that, as a buisness, they tried to give one more reason to buy those miniatures.