Yeah, the practice may not be the best in terms of historically informed performance. However, it is very much a part of the present aesthetic that values a round beatiful sound at all times. Playing double stops presents several problems, the most important of which is that an instrument playing 2 notes at once will sound about twice as loud. This creates a nightmare for dynamic balancing, to say nothing of when people try to play 3 or 4 notes at once, which can often distort the rhythm and articulation.