"I think that she is Avraham's neighbor."
Translation:אני חושב שהיא שכנה של אברהם.
I think you're imagining things. The sentences are pretty random and it's just a question of which sentences came your way. However in the first few lessons, it is true that masculine is more used, I guess not to overwhelm the learners (at least that's how I saw it) and later on it adds more feminine sentences. My experience is that there are actually more feminine sentences than masculine ones. So, both of our observations are purely subjective.
I am not imagining, thank you, I started counting how many m/f verbs there were in the word bank for "I" sentences. I will take your word for it that later on there will be more options in the word banks. And of course, when typing out the hebrew sentence, "you" can be m/f, s/pl. And all the variants seem correct.