Reb Gershon, it is wonderful to hear from you!

The Yad Ramah explains that they had no intention of going up to heaven, but what they did want was to live in a high place. There were three reasons for this:

1) Defense. They wanted to ensure their security. A high fortress is difficult for enemies to conquer.

2) Offensive warfare. A high vantage point is advantageous for launching attacks on their neighbors.

3) They wanted to worship idols. Idol worshippers select high places for their temples, as Devarim 12:2 tells us that they worshipped on "the high mountains."

However, for none of these three purposes was it necessary to build the Migdal on a mountain. It is better to build the foundations in a valley. That way, the building will be more solid and from that basis they could build the strong high building that they wanted. It is only according to what the Gemara thought at the beginning, that they wanted to reach for the skies, that it would make sense to start on a mountain, because if that was their purpose, then they would not want the building itself, but merely a stepping ground to enable them to reach Shamayim.

Kol Tuv,

Dovid Bloom