Like, from June to September, we never see new releases. I have no idea why companies don't ever exploit this time perioid - kids are out of school, people usually take time off, ect. But instead, we are forced to play old releases for whatever reason. So why don't companies release new games during the summer time anyway?

Typically Sumner months are very slow sales months. This summer, however, has been , personally speaking, an extremely busy time for game releases. I've bought Crash Bandicoot, Final Fantasy XII, Splatoon, and have Hellblade, Uncharted the Lost Legacy, Everybody's Golf, and Yakuza Kiwami pre-ordered, not to mention my want of Matterfall, Sonic Mania and Lawbreakers. So...maybe it's changing? 

Maybe because many take time off the summer to go out and do stuff rather than to stay home and game?

I know many, including myself where my summer is currently packed with a ton of outdoor events and hangouts where I dont have as much time to game.

ARMS, Splatoon, Crash, no?

I miss "Summer of arcade" on 360...

Do people usually game more during the Summer? I don't know, I'd think that since people aren't on vacation, and since the weather's colder, that they'd be at home more often, and thus play more games.

Uncharted:lost legacy and splatoon 2 are summer games .

the question you need to ask is why doesn't Microsoft release their late games in summer.

Arms released in spring btw

Although this summer doesn't look as bad as the ones past. Splatoon 2, crash trilogy, uncharted lost legacy, Mario X rabbids, yakuza kiwami, and smaller titles like tacoma (gone home devs) and matterfall (resogun devs) are there too. Also destiny 2 is practically in the summer, if you think about it.

Sony release and curate games during the full year, even a reason for some MS mockery on having the most exclusives for Holiday... so I believe you aren't looking in the right place...
Also console sales and these releases would show you that games released outside Holidays either sell less or are smaller games.