Yes, but more than that too.
Like you said,
the first reason because it's cheaper.At just $90, the Game Boy wasn’t all that expensive, and made for a perfect “big gift” for a kid at Christmas.
2nd reason : Battery lifeMel Magazine explained it best here :
Whereas the original Game Boy took four AA batteries that might last for 15 hours, the Game Gear took six AA batteries and lasted only from three to five hours.
Half the reason why parents bought their kids portable systems was to shut them up while they were traveling, and if your Game Gear died a couple of hours into a long road trip, that kind of defeated its purpose.
“Parents didn’t care about graphics or that Game Gear was color,” Horowitz explains. “Parents only looked at the initial cost, battery life and which system had more games.”
Read it more here :
https://melmagazine.com/en-us/story/sega-game-gearI know the article title is a clickbait since we already know the answer (the answer is no of course), but the article itself is good in explaining why Game Gear failed to defeat Game Boy.
3rd reason : TETRIS !!!
Tetris is the most addictive puzzle video games on earth, and on that time the only handheld that has it was only Game Boy.
Andrew Borman, the digital games curator at the Strong Museum of Play notes that Tetris — Game Boy’s top-selling game — was particularly successful across a wide range of ages.
It means not just children who wanted Game Boy, their older brothers/sisters, parents and grandparents might want it too just for Tetris alone.
