It's the easiest layout for the most part. You can just look where you need to go and run there. You don't even need a map.
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if you can navigate Windurst, there's no reason Limsa should confuse you at all.
Story Wise it makes senes since LL is off the mainland, there's not reason for the empire to be focused in that territory when they have 4-5+ faction to worry about on the mainlands. You have the gridanian's, the uldan's the Amal, the Ixal and the Coerthas inhabitants. If you want to go a step further then there is also the gridnian elementals, and the moogles.
On LL's side it's pretty much the kobold and sahagin's but even then it's 3 factions but odds are kobold's have no means to traveling to the main land, the sahagin would most likely be halted by weakening Leviathan and logically defeated Garuda should have weakened the wind around Eorzea making it harder for ships powered by wind to travel to the main content from LL while the empire most likely has more advanced tech that doesn't require on the wind.
Of course the other answer as to why LL hasn't been involved is because of bad timing, LL has Leviathan which represents flood and tsunamis while Titan represents Earthquakes, and since a disaster did occur in japan about a year ago it may have been seen as poor taste to introduce those primals and have cutscenes which involved people getting swept up by tsunamis or a quake engulfing people into the darkness below.
LL will have it's time to shine though and perhaps they will surprise us with either Levi/Titan making an appearance during 1.23. Only time will tell of course but you can be sure to see that there are a lot of secrets awaiting this final series of patches that we'll only learn about a week or so before the patch actually goes live XD.
Gridania too..... -.-
oh wait.. forgot toto-rak......
Gridania don't have a stronghold or high-level content but you think that's more important of Limsa? why?
Lack of content in all city, not only limsa
In addition to content I wouldnt mind seeing Limsa get more color. It feels a little too 'grey' / incomplete for me. Maybe more ships docked? I dont know, it needs something to punch it up....