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I'm not sure of the ratings you're looking at offhand, but the meat of the skill involves the +5% Fire Chance per Bomb hit. Having HE Rockets to pair with HE Bombs gives more value, but Rockets aren't often expected to be a reliable source of Fires.
To remark on the UK CVs for an example methodology:
Audacious lacks burst potential except on targets her bombers can full pen (UK/French/US BBs), so Demo Expert helps in providing more reliability. If the bombs cluster well, you can strike with many at a time so there's an outsized impact from Demo Expert. Double-Dipping with HE Rockets further incentivizes the skill.
Eagle should enjoy having Demo Expert for similar reasons to those above, though it provides more reliable pen values with tactical squadrons. Also, the double-dipping of torpedos can help highlight that as a damage option instead of fires which gives an alternate option for where to place your Commander points. UK Torpedoes are not the hammers of the IJN line, but they are reliable while many of the CVs in the UK line are not considered very reliable.
Malta has only HE Rockets to start fires with (outside of her secondaries which you ideally never use), so there is no need for this skill. Malta depends on Torpedoes for the general heavy lifting as the AP Bombs are mostly for citadeling Cruisers or getting basic pen damage against Battleships, so skills which accept the Torpedo capabilities are more expected.