1. growth of HSR meant less and less slower trains = higher prices of tickets, less available to poorer people
2. prices of these train tickets are actually higher than LCC airways in Europe which will transport me much faster anywhere than HSR
3. buying ticket during peak periods is very difficult
4. train station procedures take probably more time than airport procedures (even within China, much longer compared to Schengen)
5. many of not most of the HSR stations are outside of the cities, so there is no benefit between reaching HSR station and airport