Why CFL bulbs are in tubular in shape instead of being as typical bulbs?

CFL tubes work on the principal of fluorescent effects produced by electrons. Electrons emitted from the cathode in CFL tubes are incident on the chemicals pasted on inner walls of the CFL tube and visible light is produced there as a result of fluorescence. Now, since the electron beams travel only in straight lines, the CFL tube has to be linearly straight for optimum incidence of electrons on the walls of CFL device.