There are generally three reasons this scenario happens, whether you are an investor looking for a multi-unit (multi-family, three flat, etc.) property or simply a buyer looking to buy their first single family home:
1. You are choosing the type of realtors that perpetuate the industry stereotype, e.g., care more about pursuing next client than current one, extreme attention deficit disorder, lack of knowledge in the specified field ('investments' in your case), worry more about their car getting towed for illegal parking than whether or not a property meets your needs.
2. You are a fickle buyer without purpose, direction, or the ability to know when to write an offer. If you have already been through the 'primer' when you and your agent discuss what types of properties might work, and the agent is showing you places that are clearly good investments based on your requirements and you don't 'pull the trigger', then you can't expect them to stick around. They are 'donating' their time predicated on the future promise that you'll buy something. If they sense you are non-committal that means no new bluetooth for your realtor.
3. it isn't likely, but certainly possible, that you are possessed by an evil spirit, most likely some real estate investor who lost it all during the 2007 crash, and had an untimely death. He is causing this, and the only solution is an exorcism by Carlton Sheets, available for $99.95 for a limited time.