Modern yoga is synonymous with postures. Hardly any of these are described in ancient texts. They get performed for a mix of contradictory reasons, from working out (and showing off the results) to quests for internal transformation. The latter are in keeping with tradition. Physical practice began with ascetics, whose austerities had esoteric rationales. They got combined in the 20th century with health and fitness. Disentangling who does what, let alone why they do it, became more complicated.