well, most of the suits like the island ones or master of the mountain suits are just the season 11 suits with accessories and you can clearly see that on the minifigures because they reuse the same pieces for the legs sometimes and in the show in the island season you can clearly see the ninja have a full mask under the half mask and that full mask is identical to the season 11 suit. And pixel might make some or they learned how to sew idk.
After season 4 they just randomly started getting new suits also when they find Zane for the first time in dragons rising he's no longer wearing his core suit which he was wearing during the merge.
The Deepstone suits are kind of a unique example since the ninja already had the base suits at the beginning of the season but the “Deepstone armor” part was added episodes later with an actual explanation
I like to think that between Seasons 5 and 6, the ninja’s deepstone Kimonos were pretty redundant and heavy, so they just replaced the main part with the Sleeker skybound suit. Might even explain why they’re so similar.
They probably just have the suits in storage and change them when they need or want to. They change into the climber suits as soon as Lloyd decides to find Egalt because they would be useful for that trip. As for the mech pilot suits, the merge suits could have been damaged at some point.
EXACTLY I've been wondering this for a while In the new show the characters had to change from their core suits to new suits, but somehow Zane was already in his new suit when he was found? I hope they explain it haha.
In ninjago D.R. S1 It's understandable because the merge changed a lot of things, and maybe some weird thing of the merge changed their suits while the ninjas where unconscious after the merge or something like that
The dumbest example of suits is surely Lloyd's (and maybe Nya's) suit in season 9. Like.... The Ninjago city is destroyed, bikers everywhere, giant Colossus, green coloUr is not allowed anymore and by some reason this genius just somehow got a new costume💀💀💀
Maybe before Pixal made the costumes for them and other times it only improved other costumes, but nowadays ninjas probably ask someone else for the costumes or they make them themselves.