I'm not in the field but I think it's because historically neural nets were looked down and deemed unpromising because they lacked understanding, compared to Sy

I'm not in the field but I think it's because historically neural nets were looked down and deemed unpromising because they lacked understanding, compared to Symbolic AI or SVM for example. Since the Deep Learning revolution, which is engineering driven, the trend has inverted, research to understand and theory are seen as the things that hindered progress with neural nets in the past.