If you execute the apoc.load.json and look at the results, there are 70,251 records. I tried your query and it kept spinning. I add the following index and it completed in around 7 sec.
CREATE INDEX ON :People(uuid)
I would say the problem is the MERGE statements that have to look up the node by 'uuid'. Without the index this is a node scan, which takes longer and longer as the number of nodes increases.