At the time Ukraine refused to agree to it because it read so. They wanted absolute “military protection”, which none were willing to commit to, regardless of the demands they change the wording to reflect that. So by Ukraine signing it, as stated, they were well aware this would not necessarily mean the nations would provide Ukraine cover....and they also knew this would leave them vulnerable unless they built up their own military. Which they never did, and in fact it continued to deteriorate., as we all well learned during and after Crimea.
Which it stupid, since, at the very least, it would mean they wouldn't be invaded by the Russkies who signed it. That said, for the Reds, to paraphrase Lenin, agreements are like pie crusts, meant to be broken.