Ruin Explorer
Legend
Sounds to me like the OP did exactly this. He was upfront; this tank he's building is more important than roleplaying. Life is too short to NOT invest in your true passion. Someone else in the group needs to step up and learn how to DM.
Well, it's unclear, because it doesn't sound to me like he's done this. What it sounds like is happening is the OP has said "I'll DM, don't worry! Play my campaign!", and then has been repeatedly cancelling his agreed gaming sessions - not in a straightforward "No games for three months, find something else to do!" way, but on a shorter-term basis, like he's saying "Oh, we'll playing in three weeks", then a week or two later, is say "Oh, nope, too busy with tank!".
Only the OP can clarify that, of course.
No-one is suggesting he not make the tanks - what is being suggested is that he attempt some straightforward and honest time-management (which is a skill, and which not everyone has, but it's a big problem if you're promising to DM and then cancelling, repeatedly), and block out some time to make the tank, and not schedule D&D sessions in that time. I'm not sure that's hard. He might also want to say that his campaign is on long-term hiatus, and be honest and admit that it might never come back on regularly, because he prefers to build tanks.
Sad for the players, perhaps, but they can then re-arrange their affairs appropriately. Basically, he need to let them "off the hook", as it were - stop acting like he's a DM, when he actually wants to be is a tank-builder.
If, on the other hand, he wants to keep the players and run his campaign, he needs to schedule time for that, and keep to that scheduled time, unless there is an emergency (not just a choice to do something different). We all have to make choices with our time. Those choices have consequences, and you cannot expect people to respect you just cancelling pre-booked sessions repeatedly (no matter the notice), just to do something else which you could do at any time. It shows very clearly that you value that hobby more than their company and whilst that's fine, you can't hide from the fact that you're sending that message.