the amount of money sunk into r&d and the production costs would be the same regardless of whether it is a bass or a guitar.
but it is a fact that the market for bass gear is smaller than that for guitars. that is probably because bass can be considered a niche of the guitar market. market size determining the demand for the product.
rather than the variax guitar being more commercially viable than the variax bass, a more likely explanation would be that, while the variax technology itself may not be too hot, the variax guitar generates more revenue only by virtue of the guitar market being bigger than the bass market, rather than the variax guitar being a better product than the variax bass. perhaps the sales volume of the variax guitar was enough to keep it in line6's product line, while the variax bass was unsustainable.
another reason could be that with a smaller bass market, there are fewer players (manufacturers). fewer players means each player has a larger market share (by percentage). larger market share makes the brand more powerful, due to loyalty, penetration and what not. so while the bass market is smaller, the competition for precious market share would be fiercer.
