marHaba, shukran lad-dars. I think the reason why the ba-prefix is not used with the first person singular present tense (the ana-form), is because a certain degree of doubt OR personal opinion is expressed when one says " I think OR I don't think", and under these circumstances, the verb should be in the subjunctive, that is, without the ba-prefix. Salaam
العرب في عمومها و خاصة الممسكون بمقاليد الأمور لديها ،ما بتفكرش ، العرب في حالة سكر و لما بتصحى يمكن لها أن تبني ملكة التفكير لديها و عندئذ يمكنها أن تفكر.