because it doesn't prepare you as well as 114 for upper-level calculus that you'll need to take for engineering (math 240, 241, and beyond)
like the econ department says:
"Moreover, Mathematics 114 is the gateway course for the upper-level mathematics courses, while taking Mathematics 115 complicates further study of mathematics."
Advice for Freshman Contamplating a Major or Minor in Economics
or, for the simple reason that our curriculum worksheets specify 114, not 115 =p
in the same way, engineers taking physics must take 140/141 (150/151), not 101/102