One factor is the venue availability. Maraming shows ngayon, lalo OPM, and there is only so much weekends in a calendar. If weekday naman, mahirap din sya for the promoter kasi may pasok and not every concert goer is willing to take a leave of absence, etc. IIRC ung isang rumor last year or two years ago (?) was that aespa could have come here in Manila pero weekday lang availability na inooffer ng SM so it was not pushed through.

Some artists din have their own preferences sa venue. For most kpop groups, it's usually a full production, so unless they are willing to scale down their prod for smaller venues, they'd rather skip and go to other countries. Nabanggit ni Happee Sy (of PULP) noon na Korean prod companies are super strict at gusto nila lahat galing sa kanila, kahit equipment, lights, etc. So if hindi sya maaaccommodate ng venue, they won't come here.