Why is there no Starlight Celebration in Ishgard?

[Cilia]

Most likely reason: Ishgard is an expansion area, and they don't want to lock ARR only players or newbies out from experiencing it.

The same thing happens with every holiday event.

[FrightfulNight]

They could at least add decorations to make it more lore friendly. It doesn't have to be were the seasonal quest is.

[Enkidoh]

Most likely reason: Ishgard is an expansion area, and they don't want to lock ARR only players or newbies out from experiencing it.

The same thing happens with every holiday event.

This is probably the real reason - you only have to look to FFXI and see the same thing occurred there - none of FFXI's expansion pack cities like Aht Urhgan Whitegate or Kazham ever had special event decorations or npcs either, it was always just either the three starting cities or Jeuno (especially the later for the Starlight event - Jeuno would be the only city to get a special Christmas-themed remix of it's BGM and the other three cities had decorations and featured the special event npcs). SE are simply following tradition here in FFXIV.

Also, given Ishgard is still in ruins from the Dragonsong War, I think they have more pressing matters to attend to than putting decorations up.

[Zojha]

This is probably the real reason [...]

If anything, it would be the real "excuse", seeing as SE has no qualms locking ARR only players and newbies out of experiencing the zones as a whole. They're already missing out on the entire scenery, story and gameplay, so claiming missing out on a few additional decorations that aren't even unique to the area as reason not to do it has very little substance to it.
If it's indeed intentional, the "reason" would be cutting corners here - it's one less area to work with, plain and simple. And indeed, far from a first in business - at least they aren't selling the celebration as DLCs per city.

[Cilia]

If anything, it would be the real "excuse", seeing as SE has no qualms locking ARR only players and newbies out of experiencing the zones as a whole. They're already missing out on the entire scenery, story and gameplay, so claiming missing out on a few additional decorations that aren't even unique to the area as reason not to do it has very little substance to it.
If it's indeed intentional, the "reason" would be cutting corners here - it's one less area to work with, plain and simple. And indeed, far from a first in business - at least they aren't selling the celebration as DLCs per city.

Newbies not getting to Ishgard makes sense within the context of the story - the nation is isolationist and it's only because Lord Edmont is willing to let you become a ward of House Fortemps that you're allowed entry. (NPC dialogue says other adventurers are as well for their assistance during the Steps of Faith.)

There will never be DLC for this game unless you consider expansions to be as such. That's what the subscription fee is for.

There is no real reason they didn't add Starlight decos to Ishgard, but personally I'd rather they cut corners on that and finish Stormblood on time (or early!) than put some decos up in Ishgard for a few weeks.

In other words: unpleasable fanbase is unpleasable. Nothing to see here, move along.