When a spirit comes to you, there can be many reasons why. There could be something specific they feel you need to learn, you could have worked with them in a past life or they could just be interested in you. The best way to know for sure is to work with them and either ask why they came to you if your senses are developed or to notice changes within yourself over time (which is where journaling is useful).
As for myself, please keep in mind that I am still in the trenches with working with Beelzebub. It appears we met eachother halfway, in terms that we both approached eachother at the same time. The main reason on my end was because I was stuck at a point where I kept getting knocked back into the same cycles and had failed multiple pathworkings with the four horsemen, the qlipoth and working with Baal. Beelzebub was interested in working with me out of interest, as well as figuring he had something to teach me about leadership, which is a role I tend to get thrown into in life.
Since I have began working with Beelzebub, many things have changed in my personality. I am generally calmer than I was before, which helps with making decisions thoughtfully both in my leadership role in my professional life and in my family life as the head of the household. When met with stagnation though, my will to shatter it has intensified and I approach it as an enemy, which helps to serve the changes I gained while working with Belial. As I throw myself deeper into Beelzebub, I find that my nonphysical senses have been increasing dramatically, to the point where I sometimes question if I am going mad. But that has been more of a byproduct than a goal on my end.
There is a development on how I approach Belial, Beelzebub and Baal. All are different examples of how one leads and can teach a certain aspect of each. Belial is a very passionate being and it fuels a drive that inspires others to follow him instead of him demanding it. Beelzebub leads through wisdom and using teaching as a way to lead, allowing others to blossom into beings that can go on independently of him. Finally, Baal takes both approaches and combines the passion and wisdom into something that can be applied into the example of leadership many assign to a king. Without mastery of both, the kingdom crumbles, which is my best answer to why I failed based on what I learned from Beelzebub.
I also was introduced to him to a tribe of spirits that I am still figuring out. Two of those members have became advisor spirits and I have grown closer to.
I do have a journal here that I keep record of my workings with Beelzebub and how I have been progressing since I began.