Whenever I have Pelagos(the latest version of itself and all dependencies) installed the lifting train bridge is completely hidden from the tech tree and the crafting/spawn menu.

I confirmed that it wasn't any of the other submods, such as battleship and fishing trawler. Is this intentional? If so, why?

Its not a bug.

It was done so since first version of a planet.
Trian bridge is quite outdated in terms of graphics, clunky to use and elevated rails fill its role gameplay wise, so it was hidden.

I see I suppose I'm now unlikely to use your planet on my non-ships of fools world(your other mods are still great)

Could you possibly consider a setting to re-enable it(could be at the very bottom of your to-do list)

Or maybe give someone who reads this in the future permission to make a fork for that.(I'm not that good at coding)

The elevated rails argument is fair; my main reason for wanting it is for aesthetics similar to the Honk mod.

Also, there might be a canal very close to a train station(too close for a rail ramp) or a canal near already existing elevated rails

added to my cargo ships tweaks as togglable setting.