The lure of the mass market and being in Walmart or other mass retailers is very strong. Any marketer or entrepenuer would love to see their product there. Having experience working with those retailers I know that it takes a lot of resources, top logistics management, deep pockets for mass advertising and in-store promotions. On the other hand for niche products you can be #1 in your category with smaller key distribution, very clear targeting for your audience, and to focus your ad dollars.
The nice organic and controlled way to grow is to go niche, then grow to mass to help manage cash flow, generate demand and follow the product adoption curve with innovators, early adopters, the influencers, the mass and then the laggards.