Why do Gungans lack weapons that are remotely on a par with their other technologies?

Question

I was re-watching The Phantom Message for the first time last night, with my kids. During the battle sequence between the Gungans and the Federation droids, I was struck by the bizarre mixture of technologies displayed by the Gungans.

To wit: they have fairly advanced protective force-field technology. We also know from earlier sequences that they're capable of building high-tech cities and submarine transports. That's all par for the course for the Star Wars universe.

What eluded me was the reason as to why, given they seem to have access fairly advanced engineering, they're still riding animals into battle, armed with spears and ballistas that lob solid projectiles at the opposition? They don't even seem to use gunpowder. Surely this is just a recipe for slaughter?

EDIT: A couple of commenters are suggesting it's because they have no need for weapons. There are problems with this theory, not least that they live in an environment full of dangerous predatory fish. Even if that were not the case, you would imagine a society capable of building submarines would have tools that would make better improvised weapons than stone-age spears. Also, evidence from books, comics, films etc. would be useful.

Answer 1

This is covered in the film's Visual Dictionary. In short, the "Grand Army" of the Gungans is actually a holdover from their earlier (historical) conflicts with the surface-dwelling Naboobians as well as acting as a defensive force against the various large creatures that lurk in the Naboo swamps and periodically come up from the planet-core. The army itself comprises representatives from the entire Gungan nation, each contributing some of their forces to the struggle.

Long united by treaties, the Gungans do not fight the Naboo or each other. Many years ago they drove off the last invaders to threaten them. Nonetheless they maintain an armed force for tradition and defence against attack by sea monsters. The Grand Army employs both technological wizardry and traditional weaponry. Its primary focus is on defence, for which animal-mounted shield generators are used. For attack, the Gungans hurl plasmic energy balls. Soldiers of the Grand Army are inexperienced, but their resolve comes from a firm sense of duty and justice. - _{^{Star Wars: Episode 1 - Visual Dictionary}}

and

As to why the Gungan military is so backwards, this is also covered. Simply put, the Gungans openly prefer to have a society that is less "technological", enjoying a more pastoral life in their native swamps.

A fair but stubborn ruler. Boss Nass resents the arrogance of the Naboo. who regard Gungans as primitive simply because they do not embrace a technological lifestyle. He finds it best all round to minimize contact with humans.