I've been DMing a campaign for a while, and it has gone great. Unfortunately, I've noticed a trend in my style that I'm struggling to nip in the bud.
The whole party works together rather cohesively, but one player finds himself frequently talking to that important person or picking up on those small plot hooks into the larger campaign. None of the players have expressed concern yet, but he personally has gone on several side quests that the party hasn't simply because he goes more in-depth into the universe, something I feel as a DM is perhaps unfair.
By no means do I want to penalize him for being invested in the plot, but I want everyone to be able to get that level of personal attention.
How can I make sure everyone can have that full experience when not everyone is as invested?
Detail: The party met with a 3rd party separate from the villains/hero groups, and they asked for help. This player was the only one who wanted to go on it, while the rest of the party said something equivalent to "we're too busy fighting the forces of evil." The player switched to a backup who tagged along with the party, and I had a 1-on-1 session with their normal character where they helped the third party. They've also built their character to survive a lot of dangerous stuff (namely portals), so going on a single-person quests to help NPCs happens often.