Well, VIM doesn't crash :) But edge cases in general are where the bugs lurk, and 9MBs of spaces is certainly an edge case. A possible cause might be that they try to render the whole line, try to allocate too much memory, and crash when the allocation fails. Whereas if the file had many lines, they'd probably be smart enough to only render part of it.

If the editor has some built in line length limit then exceeding that limit might lead to a crash (depending upon how the editor is coded).