Too many stores cannibalizing one another.
Piracy hurts but anyone going to Astro probably is knowledgeable about it and want to patronize original video, so I don't think that's the primary reason.
Video stores are all one and the same, they carry the same stuff, serves the same customers, so opening more stores means the customer base of each store gets thinner, at some point, some store will cost more to operate than sales would allow, so they will close those stores that don't rake in the cash.
In fact, if not for the VCDs (and lately DVDs), most of these stores probably don't stand a chance against download (music and videos). The Philippine market just isn't big enough...