This space is gigantic and there is plenty of room for multiple solutions.
As others have pointed out, LinkedIn recommendations are public, which skews their content, and they are also subject to recommendation trading and general puffery.
Other interesting players are people like Xref (https://xref.com/) who automate the reference process - though to respond to your objections, these platforms are used later on in the process (e.g. on short-listing).
Many HR technologies are struggling to solve the problem you have highlighted.
They want to move from a per-employer solution ("Now that we're about to hire you, please give us 3 references") to an industry standard model ("you'll need to have a Searchlight profile to apply for this job - its a small hassle but you only have to do it once, then you can use it at any of the other jobs you'll be applying for").
Anyone who cracks that code stands a chance of becoming the next mini-LinkedIn.