Very generally speaking, hotels are often easier in concrete than steel. Depending on shape/height/size, but particularly bigger ones. Large floorplate slabs, cores with a high number of lifts. Plus at this height the sizeable columns can be 'stretched' to be thin and long and be embedded in partitions (as indeed they are here) which makes it easier to have uniform rooms and not have to have to deal with boxing out projections and what would be deeper beams above. Makes it easier to run services along corridors than under/through beams. Also a bit better sound with sound in hotels. Steel is in theory cheaper, but something like this probably more of a faff on a hotel this size.
The office block could really probably have been either, but if I were to guess, the fact the big roof to the square bridges the two, more sense in both sides being the same in terms of movement. Plus, at this scale there is a likely benefit to programme and procurement to have multiple teams and builds simultaneously, and not risk over relying of quantities of one material. Just my guess.