Curious kids, tinkerers and business customers are all other options. Someone might have an app that spams connections to annoy neighbors, someone might be testing their new program/script they wrote, someone might have malware that replicates via bluetooth connections, and yes, someone might be trying to hack into every nearby bluetooth devices. Update your network hardware (modem/routers/wifi APs), don’t accept unknown connections, and you should be as safe as can be expected (unless you’re sysadmin levels of proficient). If the annoyance gets to be too much, just disable bluetooth when you’re not using it (or make it undiscoverable so your devices can stay connected)