Islam and the Baha’i faith are extremely similar, from their doctrines to their obligatory prayers, and being partially Baha’i from a Muslim background wasn't as theologically conflicting as one would think, vs. Maybe a Muslim convering to Christianity. Furthermore, the Baha’i holy book, the Kitab I Iqan, is a commentary or Tafseer of the Quran.
So here are my reasons, I don't mean to offend anyone, and they are only personal reasons, I'm in no way trying to be preachy. :)
The primary reason for my return to Islam was the fact that everything in the Baha’i faith is controlled by the International house of Justice, a council of 9 members who regulate the practice of the Baha’i faith. This contrasts with the lack of a system of universal clergy in Islam, with religious authority resting in the Quran. The whole concept of the universal house of justice wasn't something I appreciated, and although it was primarily a personal reason, it was the main reason for my return to Islam.
What I believed made the Baha’i faith so interesting, was it's acceptance of various religious figures and texts as divine in origin. This was something I, for the longest time, did not know existed in Islam. However, after doing surprisingly very minimum research, the Baha’i concept of a universal religion not revealed only in the Middle East was also made apparent to me in Islam. In fact, the Quran says in numerous verses that God revealed his/her message to various prophets in every nation and time. So what I thought made the Baha’i faith different from Islam, was really just my lack of knowledge on Islam.
Information on practicing the Baha’i faith is difficult to access. Unlike in Islam, where you can literally just search up how to pray, fast, give charity, and you'll get the how tos and everything; accessing that same information for the Baha’i faith is a lot harder, in fact, I didn't realize the obligatory prayers in the Baha’i faith had movements (I thought they were only words) until I read an article on Wikipedia. My bad :)
Prayer in congregation is forbidden. Now I do like praying by myself, but I also feel a lot more connected when praying with a large congregation in a mosque. However in the Baha’i faith, praying in congregation is strictly forbidden, I'm not so sure why, but it is, and I did not see any reason for it. I also believe congregational prayer helps in fostering bonding in the community.
Manifestations of God worship God??? This reason would technically be 2nd, and is a very theological reason for me not believing in the Baha’i faith anymore. I never really understood why the manifestations of God themselves told us to worship God, and why the manifestations strictly prohibited the association of partners to God. For example, prophet Muhammad in the Quran is referred to as merely a human, yet in the Baha’i faith, he is the final manifestation of God from the Adamic cycle. I never really understood how that made any sense, and I thought prophet hood was more reasonable.
And those were just a few but major reasons for me going from Baha’i to Muslim.
Hope this helps!