Answering digibochur: One reason may be b/c the kind of people who’d want to live in Modiin Illit are less likely to be on this forum.
Where else is there climate similar to (or cooler than) Yerusholayim? What is Beitar like? Tel-Zion?
What kind of crowd live in the newer areas of Telz-stone, eg. Achuzat Ye’arim?