Because I don't differentiate between miracles of true Prophets and don't deny them or claim one was symbolic and the other wasn't, for they are performed by a power bestowed upon them by an Omnipotent God. However Baha'i belief states that these miracles are superstition because they are unscientific:
"If religious beliefs and opinions are found contrary to the standards of science they are mere superstitions and imaginations; for the antithesis of knowledge is ignorance, and the child of ignorance is superstition." –
Abdu’l-Baha,
Baha’i World Faith, p. 239.
Yet, they claim that some of these unscientific superstitions are true, but only they are the one's that can recognize which unscientific superstition we should believe and which one we shouldn't. Which sounds kind of funny because if it's an unscientific superstition based on baha'i teachings, it's an unscientific superstition. They have to deny all miracles and some of them can't magically turn into facts and be acceptable.
Baha’u’llah didn’t like talk of miracles because it degraded the Cause of God to a circus. When He was asked by the religious leaders to perform a miracle to prove His validity as a Manifestation He agreed on condition they accept Him once He performed it.
Bahá’u’lláh replied, “Although you have no right to ask this, for God should test His creatures, and they should not test God, still I allow and accept this request. But the Cause of God is not a theatrical display that is presented every hour, of which some new diversion may be asked for every day. If it were thus, the Cause of God would become mere child’s play.
In the end they couldn’t decide on a miracle and didn’t push the issue further because of fear He would produce it.
The fact He agreed to perform any miracle of their choosing surprised those who challenged Him when He agreed to accept their demand.
The ulamas must, therefore, assemble, and, with one accord, choose one miracle, and write that, after the performance of this miracle they will no longer entertain doubts about Me, and that all will acknowledge and confess the truth of My Cause. Let them seal this paper, and bring it to Me. This must be the accepted criterion: if the miracle is performed, no doubt will remain for them; and if not, We shall be convicted of imposture.”
Baha’u’llah, being a Manifestation of God knew He could perform anything they asked so it was just up to them to choose and they got scared and backed off.