an editor has revised a sentence of my article. I would like to figure out the reason for the changes. Please see the sentence below.
Original Version This operation has been a fundamental cause of the exacerbated wage disparity, excessive investment in property, abnormally high leverage rate and asset bubble.
Revised Version This operation has been a fundamental cause of the exacerbated wage disparity, excessive investment in property, and abnormally high leverage rates and asset bubbles.
(Changes he made) (1) He added a 's' for the countable nouns 'rate' and 'bubble' (2) and then added the conjunction 'and' before them.
Is this because he would like to separate these two plural countable nouns from the preceding abstract nouns, 'disparity' and 'investment', which are in uncountable form? Is this necessary, and is it grammatical to put 'and' before the second last noun rather than before the last one? Please kindly advise. Thanks!