Hi Israel is great! I think the reason that no one answered you before was that most forumers here use Bar-Beret for general discussion, and few visit the 'main' Israel forum.
Anyway, to answer your question about Ramat Gan: The issue is rather complicated, and I don't think either I or Hebrewtext will be able to give you a 100% correct answer.
Basically a few decades ago the business center (CBD) of Tel Aviv was in souther-central TA, where the Shalom Meir tower is. After that everyone thought that the CBD would move closer to the sea, in an area called Manshiyya (near the Neve Tzedek neighborhood), and started developing that area. But people didn't come en-masse, because the area was horrible in terms of transportation, both private (no parking), and public (long bus rides, constant traffic jams).
All the while, Ramat Gan already had a small successful business center started beforehand by a diamond entrepreneur, with great transportation (Jabotinsky and Ayalon main roads + railway) and it was only natural to build and expand on it while the already-crowded Tel Aviv was trying to decide what area to develop next. Because Tel Aviv has so little open area, it's very difficult to plan an entire new neighborhood, while in Ramat Gan it was simpler and the municipality was generous in granting building permits for tall towers in the area.
Despite this, Tel Aviv is starting to develop an area near the Ramat Gan diamond exchange called TLV2000/TLV Loop, which will feature a tower possibly taller than Ramat Gan's 244 m Moshe Aviv/City Gate tower. Again, the main basis here is transportation, and the idea is to develop an area easily accessible to all forms of transport.