I couldn't find anything related to your question but the 35 x 35 mm tiles in the Demo Spiel or Carcassonne for Two, for example, make me think the tile size is an arbitrary decision that is also linked to the size of the meeples.
My intuition tells me that, in the end, it may be related to the trade-off between production cost per unit vs. perceived value and therefore a "reasonable" sale price according to the latter. You can also see this reflected in the size of the boxes vs. their actual content... specially with Big Boxes.