Of course at that point you're already bought into the ecosystem with physical samples (which are not cheap), monitor calibration and all, so it feels like a "double dip" for no value added
It's not really a double dip. It's more like a triple dip, as they charge the designers for the physical samples, then they charge the designers in order to reference those physical samples in their Photoshop designs, and then they charge the printers in order to produce the output that the Photoshop files are referencing.
They want to make sure you pay at every single point where you might think "PANTONE®". So in addition of having to buy the PANTONE® sample book in order to actually know what the PANTONE® colours are, you now need to pay to reference the PANTONE® colours in a Photoshop document so that the receiving party knows which PANTONE® colours they need to get out of a printer.
If they could make you pay for sending an email containing "I need the background to be in PANTONE® Red 032 C", they would.
I would argue that a multi-sided marketplace isn't always a double dip. If I want a Pantone 628 C coffee mug from China, I can order it and know exactly what colour I'm getting. It saves designers tons of money and time with avoided back-and-forth in the prototyping process.