Wellesley Court is a large development of around 150 flats, so there are not actually that many properties for sale.
The managing agents have been proposing for some time to complete major works, and have been building up a sink fund over the last five years. Service charges need to cover lifts, porters and communal areas, so some leaseholders may be struggling to find the extra funds to pay the major works fund.
Wellesley Court is much cheaper in terms of £/sq.ft than neighbouring properties. Once the major works are completed, the block will become more desirable and there will be an uplift in values, reducing the differential with it's neighbours.