In Europe, a huge driver for standardization of timezones into "reasonable" slots was railway traffic, including cross-border traffic.

Railways are extremely sensitive to exact time and, indeed, the very concept of unified time across the entire region or country only started developing when railways expanded across Europe. Prior to that, individual towns were happy with their own local solar time, but once railway connections were introduced, time irregularities would cause chaos at best and carnage at worst. That led to introduction of unified railway time which developed to timezones as we know them.

Railways aren't as prominent nowadays as they were 100-150 years ago, and countries like Nepal and India don't have extensive, frequently used cross-border railways anyway; any cross-border traffic is sporadic and mostly freight. So there is one fewer reason to cooperate with your neighbors when it comes to time-related issues. Trucks can take weird timezone changes just fine.