Strange behavior from frequency to angular frequency in FFT
This is probably the single most asked question on this forum. A similar one was asked  and answered just a few hours ago: Spectral leakage from mathematical point of view
Your expectations are wrong: you only get a spectral dirac impulse if the frequency of the complex exponential on he FFT grid, i.e. an integer multiple of the sample rate divided by the FFT length. In your case you have $N_{FFT} = 10000$ and $F_s = 1000$, so your FFT bin spacing is 0.1 Hz. 50 Hz is an integer multiple of 0.1Hz but $50/(2\pi)$ isn't and so the energy will spread out over the adjacent bins.
A different way to look at it: the DFT assumes that the time signal is periodic with the FFT length. Since your exponential does NOT have an integer number of periods inside one FFT frame, the periodic repetition creates a discontinuity at the frame boundary