About that $60 thing... Ever notice how almost all new games, even crappy little shovelware affairs, come out in retail stores with a $60 price point? That's because the publishers essentially demand that retailers sell games at that price, else they'll cut them out of the loop on future things by not selling them games. Retailers are cool with that because the lack of competitive pricing means they don't have to cut into their own prices to bring in customers, because video game buying consumers know that new games are always $60 so they're gonna come in prepared to pay $60. Also, Sony and Microsoft sell digital copies of their games on their own little store platforms for $60 as well, which is just them raking in profits because all the money that would go to shipping and packaging and the retail cut goes right to them.
DLC doesn't exist to keep prices down at or below $60. DLC exists for the express purpose of being able to make more than $60 off those games despite the publisher/retailer agreement on prices. A huge bulk of DLC that exists is just cosmetic stuff, pure cash grab things, not things that actually add to the gameplay. It's also not so much about size either: multiple disc games have been a thing for a long damn time, and having game files that are a few GB bigger for customers to download won't be a huge drain on any reasonable game server. It's absolutely a money thing before any other considerations. Some companies do it well by sticking to a similar formula as expansion packs in the past, offering additional game content for additional money, but most just crank out cosmetics to make money off of people willing to pay $5 for a new look for their character.