The WVTP had no plans to go completely cashless at any of their toll plazas just a few years ago, as the EZ-Pass rate was comparably low compared to other toll highways. Most traffic is not local and those types of drivers more likely than not do not have EZ-Pass. As of this year, it looks like the ETC rate at the mainline plazas is 55%-62%.
The North Beckley Plaza is more commuter-dependent. It's cheap, and even more so if you have the Single Fee Discount Plan ($25/year for unlimited travel), which has led the EZ-Pass rate to dramatically increase. There isn't a good reason not to use EZ-Pass there if you live in the area, and using the Turnpike to bypass Beckley saves so much time.