It's never a good idea to compare yourself to anyone and wonder why you aren't having the same sucess as them. At the end of the day you aren't them and they are already doing themselves better than you ever will. Only compare you to yourself.
I like that you are drawing women that looks like they have internal organs and aren't afraid of natural skin folds. You need to work on what your images are saying. Sexy is a lot about presentation and context. A scantily drawn character with large breasts isn't immediately sexy. You need to put more emotion and narrative in that. That said I like your cute scenarios here, the bubblegum and pudding girls are in the right direction. Just put some more thought into this. Your rendering has many levels but they tend to stick towards the edges of the form and flattening it. Be bolder here and and follow the form, keep in mind where the light is coming from. Lastly, don't avoid feet. You won't learn how to draw them if you do. The composition in Summer Stretch is great. Keep in mind how you place things and don't be afraid of backgrounds either.
Oh no, I'm not bothered about his success D: Its the audience. He has many female watchers while mine are mostly male.
Thank you so much for your comment, it really has changed my perspective on my artwork and has given me more of a drive to do better. I now know the main parts of where I need to improve. Thanks again <3
Well speaking as a woman who is partial to the occasional boob, your stuff feels male-targeted. It's the poses: they're quite submissive (elbows in, eyes down) and "lad's mag", not much more to the image composition other than the scantily clad lady. It's not necessarily how a female veiwer wants to imagine themselves.
For instance, I noticed that the person who tried to correct the impossible bikini in Summer Stretch was a woman. I knew it before checking their profile because I (as a person with boobs of size enough that structure in a bikini is really important) had exactly the same thought as her and found the garment distracting. If you're interested in designing pinups that appeal to women, you should think about your own female experience and your expression of your own sexuality and notice how it differs to portrayals of women in male-targeted media.
I also think you could focus more on creating "fuller" illustrations that have other design elements than just the figure. If they have aesthetic appeal beyond the nudity then naturally this makes it accessible to a broader audience. In most of your images currently, it is just a figure against a black background.
You have to remember that a woman looking at a pinup generally identifies with the girl in the picture. If the girl in the picture looks like she does nothing with her time except stands around being looked at, well, that's not exactly a hot fantasy for most women. Slugbox has more pictures where it looks like the subject is in the middle of doing something and the artist just happened to take a picture at a sexy moment. Even the simple "standing around" pinups have a wider range of emotions.
He also has a better grasp on cuteness. Your work suffers a little from overly-long noses and mouths too far down the chin.