In recent years particularly, horror has often been the domain of the major franchise. Stumble upon a winning concept - a yearly day of lawlessness, for example, or a simple haunted doll - and more often than not, studios will milk the idea for all it’s worth. Horror audiences are a dedicated bunch, and often not in possession of the most discerning taste. Churn the films out and watch the money roll in.
Simultaneously, the more inventive creatives have always found the genre lends itself to a low budget. Exploiting a viewer’s fear doesn’t necessarily require stacks of money and costly effects. With the right premise, you can come out with a spooky spectacular on a shoestring.
These movies may not have had the backing of a studio, but in horror, ingenuity and craft will usually triumph over a colossal budget (though several of these films were prestige pieces with decent money behind them - small potatoes, relatively speaking, but a decent chunk of change all the same).
Horror can be a real meritocracy - the idea is scary, or it isn’t, no matter the studio backing or lack thereof. These movies prove that the concept is king.