RPGMemes

That sounds like a pacing issue. Out-of-character the group might agree that there's a desire to do side plots, but in-character a (heroic) party that is aware of a great evil is going to take actions in the interest of stopping that evil, even if they're knowingly unprepared (plucky young heroes who win against overwhelming odds are the stuff of legend, after all.) This is why it's important to keep scope small at lower levels - as tempting as it might be to daisy chain a much bigger bad to a smaller one with a cryptic note or mysterious secret symbol so that you can do an "all according to plan" speech later, if you drop a plot hook, the players will bite on it with the force of a million industrial hydraulic presses and not let go until the whole mystery is unraveled.

Also, don't pull a grey-and-black gambit on the party unless it's what the plan was all along and the party has been aggressively ignoring the other bait. As a player, one of my biggest pet peeves is catching shit for doing what I thought the DM wanted us to do with the narrative they laid out. It's right up there with a "mastermind" villain who is obviously ass-pulling contingency plans when the players do shit the DM didn't account for. Protip to anyone reading: if your villain needs to have plot armor so the plot can continue with zero hitches, they're not a very good villain, and it's not a very good plot.