While the audit administration building was certainly 'under construction', the Ghost Tower isn't exactly completed so technically (and arguably), both are still 'under construction'. The latter has been exposed to the elements for decades, which should've weakened it, but it is still standing tall and erect against the test of time and mother nature (literally). Also, since the Ghost Tower was nearer to completion, its structure would've had to bear more weight than the audit administration building which doesn't have the weights of claddings and finishings added to it yet. So while the derelict continued standing even without care or maintenance, a spanking new building that was supposed to be built using more modern techniques, materials and technologies collapsed like a house of cards.
Oh, and as one poster here mentioned, it's just one of the many tall buildings in BKK that did not collapse.
'The Chinese didn't build the Ghost Tower' is the simple answer, but I think the issue runs deeper than that and the corruption that surrounds the development and construction of the collapsed mess.