Couple of reasons. The first was to eventually replace the few hundred T-55s and T-62s and then possibly some of the older M60s that were upgraded to M60A3s. A lot of those tanks are very old.
The other big reason was that it was to be a ToT contract which would open up jobs and bring more tank assembly experience to Egypt. There was also a rumor that they might be a gateway to introducing a market into central African countries through Egypt, but I think that was only a rumor.
The 1967 war and especially the 1973 October war proved that tanks are critical in defending the Sinai from land-thieving enemies. So the Egyptian Army puts a lot of stock into tank warfare which makes up a huge part of the rapid response forces. That branch was created strictly to rapidly push armor of all types and specifically tanks across the Suez Canal to stop and prevent another invasion of the peninsula. Hence the emphasis on a very large tank army as well as other armored vehicles of all types.
