I read that Robusta production is increasing in many 'only aribica' countries. Is it 'low brow' because of lower profit margins or it is so lousy I should never let a sip cross my lips?
Because they are low brow, that is lower quality and much less desirable. Robusta beans are generally regarded as inferior to Arabica and command about half the price. Many coffee producers will proudly proclaim that their coffee is 100% Arabica as a hallmark of quality.
Arabica beans produce a richer taste and have a better balance of sweet acidity. Sugar, fruit, berry and chocolate flavours are common and the characteristic winey taste of higher of higher quality coffee is due to Arabica's excellent acidity. Also the much remarked upon and pleasantly appealing aroma of roasting coffee is due to Arabica beans. Brazil is the largest producer and Arabica beans represent 75% of all coffee sold in the world.
Robusta by contrast has a stronger, harsher full bodied and more bitter taste with a grainy flavour profile and earthy or peanut aftertaste. Traditional Italian espresso blends typically incorporate about 10% Robusta because Robusta beans create more crema. The majority of Robusta beans go towards the bulk manufacturer of instant coffee where price trumps quality concerns.
Robusta beans contain more caffeine, are easier to grow and produce substantially higher yields. Vietnam is the largest producer.