Currently it is relatively difficult to move data from one (open)cypher implementation to an other. Also as support is uneven for all features it is not so simple to get started on Neo4J and then evaluate e.g. TigerGraph if you find that Neo4J is not ideal for your usecase.

If your application only uses GQL then you could start on Neo4J but after two years in production cheaply move to a competitor. By just switching your backend and run your test cases etc. your data did not change, your queries remain the same, so evaluation is relatively straightforward.

I see this quite often in the SPARQL world. First few years of a product is with engine A, then some annoyance in production show up. Engines B-D are evaluated and a different one is chosen. Or sometimes both are run at once for different query workloads on the same data. Which is relatively cheap in the SPARQL environment. But because of custom engineering in the property graph world to move from engine 1 to engine 2 it is much more expensive in engineering hours.