That's just how it is. The imperative (used for commands/directions) of "gråta" is "gråt". I find wiktionary really helpful for checking conjugations: https://en.wiktionary.org/wiki/gr%C3%A5ta#Swedish
I think the general rule is verbs that end in -er in the present tense (e.g. 'Jag gråter') lose the -er to form the imperative ('Gråt inte!')
If you were making a joke about "don't be be dull, do research!", then I'm sorry for the grammar bit ;) In that case, I think it would need to be "Var inte grå..." but I don't know if that actually scans in Swedish.