The reason that they're so dominant is because they actually are that much better. Inertia obviously matters, but outside of GOG prohibiting DRM (which in many cases results in customers being stuck to much older builds of the game), you'd be hard pressed to find even single features/traits other platforms do better.
Steam Workshop, not just ratings but also discussion forums and places for guides and other media, proton (which they chose to collaborate and pay for development of an open source project, rather than using their massive bankroll to redo from scratch, but other platforms still can't be bothered to use for free), big picture mode, Steam input, etc. Instead of resting on inertia, or abusing their market position to make competition more difficult, they just keep improving their platform. They even let developers sell Steam keys for their games for free (with some restrictions that only seem to be applied in obvious abuse scenarios), without taking any cut.
Gamers refuse to go elsewhere in large part because other platforms are a lot worse.
There are a bunch of free channels on the internet that some TVs can just stream without a dedicated app. These channels are supported by ads like cable/whatever channels, but not locked behind a subscription. VLC is supporting whatever formats they use to allow (or make it easier; IDK) people to watch them if they want.
The other part is that they're working on web assembly to allow sites to use VLC as their embedded video player.
A game having a significant sale 6 months or a year later is perfectly normal behavior. It tells you absolutely nothing about the industry. It's worked that way for decades. It's not the tiniest bit unusual.
Discounts over time are a perfectly standard part of their pricing strategy. It's not even mildly unhealthy. Resellers don't count at all, because that's always their strategy.
The unusual part of suicide squad and skull and bones is that they're brand new games. The discounts are not huge because there's a problem with the market. They're huge because they're dogshit excuses for products and nobody is stupid enough to buy them.
The other benefit with Costco is that they have an extremely generous return policy.
Some obvious stuff has different rules (electronics is 90 days, stuff like tires that have clear expected lifespans have their own rules), but it is extremely liberal. And my experience is that I pretty rarely have to use it, because while not everything is a premium product for a bargain price, they tend to ensure that the suppliers for products they sell have reasonable build quality and make stuff that isn't trash designed to fail.