As Greg stated there is the questions of economics, quality of gear, knowledge of it’s condition and the comfort of familiarity with your own gear. With exposure protection 2 suits of equal material and quality can give totally different dive experiences because of fit issues. When purchasing invest the extra time to shop for a fit that minimizes air pockets and is skin tight with minimal stretching. Extra details such as a better zipper with a thick back pad to help seal, wrist seals and ankle seals can help with water control as can a lining such as merino wool. The differences in these details can keep you much warmer in colder waters and allow for extended dive times.
There is also the issue of convenience...You may find the option to dive comes up more if you don’t need to head to a shop for rental gear. Last minute opportunities to dive on a Sunday when you local dive shop is closed or night dives after hours are no problem when you own your gear.
Even those of us that do own complete outfits often find ourselves picking and choosing depending on travel arrangements. If I drive to a dive trip I bring my own tanks so I can have extra capacity. The only time I bring weights is for local diving. I do log 50-100 dives per year.
It all depends on your budget and what you value for your dive experiences.