Possibly because the 1.5TSI is a hugely oversubscribed engine from VW, eg...I guess they will first go VW (Golf, Passat, Tiguain, T-ROc), then Audi (A3, A4, A5, Q3, Q2), then Seat has to share the rest with Skoda, who has it in the Scala, Karooq, Kamiq. At least Seat has this engine for the Leon,
Ateca,
Tarraco, and some Aronas. None for the
Ibiza since awhile. If it's any consolation, Polo's and Fabia don't get it either. The new Audi A1 might, not sure...
In my home town in Singapore/Malaysia, they don't even offer the 1.5, still using the old 1.4 ACT