Consumer payments-focused startups Klarna Bank AB, Afterpay Ltd. and Affirm Holdings have a had a good run at changing how people shop and growing rapidly until recently. Now, much bigger players look like they’re gearing up to streamroll the little guys. 

Apple Inc. launched an installment-payments feature Monday among a string of product updates. It’s a prime example, along with JPMorgan Chase & Co., of big tech and finance incumbents turning their attention and investment dollars toward areas that young companies have made their own.