I never really understood people who played the game FOR the Gjallarhorn.

Because Gjallarhorn represented power for many people.

Like if the reason your playing is hoping you get lucky enough to get a certain weapon then idk, seems pretty shallow.

You have to remember that this is a loot game and things like MMOs strive off the grind. For many they do specific quests, missions, stages, events, whatever for the loot. It also adds a thrill to every drop chance. Similar to loot crates where I doubt I am the only person who hopes the next one has blank specific item I want.

Where Destiny went wrong, which is what this person is somewhat getting at, is Bungie decided to take away the end game grind. None of the desired weapons in year 2 or 3 were obtained via RNG. Dark Drinker, Raze-Lighter, Touch of Malice, Black Spindle and Gjallarhorn were all obtained through quests or specific events.

This is why Ice Breaker was praised by many, since it returned an element of luck to getting fantastic loot. It wasn't enough to just do the Nightfall fast, you needed to get lucky and then you got this super special gun.

Personally returning to the vault to open that mysterious portal that never seemed to have a purpose and finding "The 7th chest" is more engaging and interesting than rolling dice on an activity you've done dozens of times.

With that being said, it's all perspective. How exactly is this different than chasing a specific item? You're essentially doing a task and looking for a reward. The only difference is that yours is a little more conceptual (solving the mystery) than power (Gjallarhorn).