Is this part of paragraph that lists many reasons or one main reason?
Either word (reason or reasons) can be used.
People can grow their own food in the country. The pollution in the big cities is becoming a health hazard. In short, people will have less reasons to travel to city centres from outlying areas.
"Reason" can be countable or uncountable, depending on its meaning. In the above sentence it means "motivation" and is uncountable (so you can't put it into the plural).
And to be perfectly correct, you use "less" with an uncountable noun (as above) and "fewer" with a countable noun (fewer reasons).
(More and more, however, people are using "less" with both uncountable and countable nouns.) :-D:-D
Could you please explain to me the meaning and structure the (I am not sure if I should use 'the' here) another sentence with 'less', I cannot understand the last part (which started with "as less social contact...")
This, in turn, may affect the social atmosphere of an organisation, however, as less social contact with one's colleagues could harm morale and loyalty.
(It seems to me you are so good at this topic )
Maybe it's the word "as" that's confusing you? In this context it means more or less the same thing as "because".
So you could paraphrase this subordinate clause more or less like this:
"....because colleagues wouldn't be seeing each other so much and this could affect their level of confidence and their positive feelings, also their loyalty."
Hope I've answered your question?
(Incidentally, in you message you say "I am not sure if I should use 'the' here". No, not 'the' but 'of'.) :-D:-D