For aerospace engineering (and mechanical engineering) you currently need a minimum 3.8 college GPA to transfer. As to why those are so popular these days, I do not know except that it may have to do partly with number who accepted the offers of admission rather than just higher popularity. They use past yield experience to determine the approximate number they are going to admit to get a desired yield and not overload (or underlaod) the department. The yield percentage for freshman engineering overall went up somewhat 0ver the last five years but kept increasing at a higher rate than overall for mechanical and aero and thus they kept admitting a somewhat lower percentage in those majors but it still presented annual 'surprises" leaving each new class for those majors overloaded and thus lowering the chances of a transfer later being admitted.
Currently, you have one and only one oppurtunity to transfer to the business college from DGS or any other UIUC college -- at the end of first year to begin in sophomore year. (Transfer into other colleges can be be attempted after first or second year and for a number of majors mid second year or even later than after second year.) The business college decides whether you can transfer after second semester freshman grades come out. Usual transfer acceptance rate into business college from the other colleges is about 50%. High grades are needed but they are no guarantee because the business college is truly a full file review college for which essays and ECs actually are important with the result that some with very high grades get rejected and others with seemingly low grades (but still in the 3s GPA) are accepted.