Ethics of Spinoza - est ut

Est, ut can indeed mean something like “there is reason to,” and conversely, when negated, something like “it is unnecessary.”

This applies to non est, ut (+ subjunctive) and similar forms like: non est, quod (+ indicative or subjunctive) / nihil est, quod / nihil est, cur etc. All these mean “there is no reason, it is unnecessary, not worthwhile.”

I cannot comment on the Oxford Latin Dictionary, but Lewis & Short give (I.B.5.b.α):

Also, est ut, there is reason, that

(Note: Perseus completely messes up the structure of that article. It is much better displayed at Collatinus-web, but I do not know how to link articles there, so you have to look it up yourself.)

One example they give is indeed negated (translation from the Latin, however, by me):

neque est ut putemus ignorari ea ab animalibus
there is no reason for us to believe, perhaps even: we should/must not believe

If you can read German, Georges (I.B.d) (also available at Collatinus-web) is even clearer and mentions the negated case quite explicitly (translation from the Latin, where given, by Georges, and from the German by me):

however, non est quod or ut etc., or nihil est quod or cur, there is no grounds, I (you etc.) have no reason to etc., nihil est, quod gestias, Cic.: non est igitur, ut mirandum sit, so one need not wonder, Cic.