I think there is a point of sale and marketing aspect to this assuming you're asking for business reasons. Sort of a "what matters BEFORE the book is sold VS what matters after the book is sold." Not necessarily the same answer?
When you're talking about selling a physical book, you can watch people flip through. They seldom stop on text or rules and often stop flipping at the art. If, as a publisher, you're selling physical copies at cons or in brick and mortar stores, I think you kind of HAVE to have a good amount of art. Paizo once noted you need a graphical element every 4th page at minimum. The idea is that anyone flipping through will see something other than text. Now this could be a chart or sidebar, but it's usually art. Art is also vital to selling online. If you're going to engage people on social media and the other 'markets' where RPG folks have to sell today, I think you need a pool of art to sell with.
When you're talking about selling a physical book, you can watch people flip through. They seldom stop on text or rules and often stop flipping at the art. If, as a publisher, you're selling physical copies at cons or in brick and mortar stores, I think you kind of HAVE to have a good amount of art. Paizo once noted you need a graphical element every 4th page at minimum. The idea is that anyone flipping through will see something other than text. Now this could be a chart or sidebar, but it's usually art. Art is also vital to selling online. If you're going to engage people on social media and the other 'markets' where RPG folks have to sell today, I think you need a pool of art to sell with.