Distribution stopped being the hard part.
The venture model that worked from roughly 2010 onward was built around a single insight: software had near-zero marginal cost, so whoever reached customers first and cheapest compounded fastest. Capital went into go-to-market because go-to-market was the constraint.
That advantage has largely been competed away. Building and shipping software is now cheap enough that a product lead no longer lasts long, and the channels that once produced cheap growth are saturated and priced accordingly.