Most simply the smaller the increments, the more you pay overall per piece. I don't mind kits solely because they are still bundles and bundles for $5 USD, which is not unreasonable for my budget.
On the other hand, as someone that still plays 3, the store is quite expensive at asking price and requires a premium currency (a mobile esque microtransaction requirement I despise) which requires you to put so much money in to even get started. Further, especially speaking about using the store now, not only is it not as easy to get the old discounts and free Simpoints (which was a decent task in of itself from what I understand to get a bunch of things at a nice price) but the infrastructure and customer support is currently lacking. Many people, including myself, have had issues with the site that Origin support or anyone else cannot seem to help with.
The only real benefit to the store was that it got regular content and often. Which is enticing, I cannot deny, but it is no where near enough to wish we had a Sims 4 store instead of kits. Especially since four kits were announced this month.
Edit: I've seen a few mentions of worlds for sale on the Sims 3 store, which I understand being seen as a pro for the store but I see it more as a pro for 3 in general. It technically isn't impossible that 4 would sell worlds piecemeal still, but I genuinely think they would have world kits if 4 could handle it. Why not charge for something people are begging for and cannot make since there is no CAW tool this round?
