Everyone trying to fathom the difference, here is a very good hack mentioned in the given below url courtesy
Magoosh:
EXCERPT:1) We use “greater” when the noun in question is a number. Some examples of nouns that are themselves numbers are: percent, interest rate, population, volume, distance, price, cost, and number.
e.g.) The area of Georgia is greater than that of Pennsylvania.
e.g.) The price of a trip to the ballgame is greater than the cost of a night at the opera.
2) We can use "more" for
both countable and
uncountable nouns, depending on the context.
e.g.1) Holland has more tulips than does any other country in Western Europe.
Tulips are distinct and countable: you can count how many tulips you have.
e.g.2) The US State of Georgia has more land than does the state of Pennsylvania.
“Land” is an uncountable noun.
e.g.3) It costs more to go to the ballgame than to go to the opera.
Here, the implicit noun is “money”, which is also uncountable (as opposed to units of money, such as dollars, which are countable).
For reference:
https://magoosh.com/gmat/verbal/sentence-correction/gmat-comparisons-more-vs-greater-and-less-vs-fewer/