He moved up and the position forced him to become so bad. That happens a lot.
That's the thing: In the movie, he was acting out of personal malice rather than the job forcing him to be a jerk. He was in fact going against his own ministry's policy just to satisfy his grudge. It was pointed out during the final round of negotations (when Anzu brought the Tankery Federation chief, Chouno and Shiho to back her up) that his insistence on closing down Oorai's schoolship despite its tankery team winning the tournament against all odds will actively harm the future of Tankery as a Japanese sport (and by proxy, Japan's own standing as it's going to host the sport's upcoming international tournament), by driving away girls who would've otherwise decided to pursue tankery as a vocation and giving current practitioners a strong reason to quit early, because Tsuji's actions as a MEXT official make said ministry look like it considers tankery worthless.
His own reaction to that argument didn't look like he was remotely surprised by the consequences of his actions; rather, he seemed more concerned that he can't give a counter-argument to it. In other words, he knew exactly what he was doing, what it would lead to, and did it anyway. Obviously he was hoping that nobody would think deeply on the ramifications of the Oorai school's closure.
Honestly, I was surprised that the movie didn't end with someone from higher up the government chain of authority coming down to the match's field just after Ooarai et al. won in order to demand from Tsuji an explanation to what s/he had just discovered, and then telling the idiot that he should have his resignation letter delivered by tomorrow for his abuses and overreaching of his office's powers and authority.
... WAIT, HOW CAN TSUJI BE THAT GOOD OF A PERSON BACK THEN AND THEN TURN INTO A SLEAZY SELF-IMPORTANT ASSHOLE IN THE MOVIE'S TIME FRAME?!
If you remember he only has it in for Ooarai so that, "the funding can help keep the other schools going". He didn't teach and thus doesn't care about any Ooarai girls, so he sees it as a chance to help those he did, (much like personally getting Anzio a P40 earlier in this comic). This dosn't excuse how much of an arsehole he becomes mind.
Imagine if this comic was building up to the series with getting Anzio more money being the motivation.
Ribbon warrior also mentions how Ooarai's victory changed tankery in itself in a way the senshado federation wasn't exactly happy about, so perhaps he was ordered to make sure Oorai closes so it doesn't spiral further out of control. The latest chapters really show how Oorai affected the other teams.
Nooooooo!Today, chairman-sensei will be leaving our kindergarten.I'm sorry. A friend asked me to help with a different job.We'll see each other again-Katyusha says you can't go so you can't go...!...Thank you, Mika-chan. I look forward to it.Can you hear it, Sensei?Hip-chan, it's the chairman who is leaving.Chairman-sensei.Hm?What is it, Mika-chan?*Sniff**Sniff*Ooarai vs Selection University battleMika... is going to get better at playing the kantele...
When I grow up, I want Sensei to hear it.*Twang*... *Twang*... *Twang*...So buy my see-dee when I put it out, okay?Sure.Now could you please give me back the bag you're hiding in your hat...?But you'll leave if I give it to you.This sound...The wind will carry a gentle sound anywhere.... My, she's improved..... What could you be referring to?