I'm a believer that although this is not a cause of hairloss in it's own, using massive amounts of gel, hairspray, etc. But if you are prone to hair loss, and it's in your genes, using massive amounts of hair styling products does make the onset a little earlier. I know there was always this one spot at my hair line which I always tried to tame with using lots of hair spray on that one spot. And that is the first spot where I saw on my head that started to bald. But also I know someone that never used hair styling products in their life, and started losing his hair at the same time as me (I pretty much grew up with him). And I know someone that uses massive amounts of hair styling products and has the thickest fullest head of hair. So in conclusion, the number one factor is hereditary, but the enviroment which you subject your scalp to is a secondary factor.
Remember it's not a fact, there have been NO scientific studies that proves hairstyle products cause hairloss. My conclusion comes from my own reasoning and judgements.