A lot of the negativity comes from people who missed the boat, sold too early, etc. Also, people who don't understand bitcoin or confuse it with ICOs/blockchain crap. I'd say that's the bulk of it to be honest.
Having said that, I think there's a bit of (healthy) skepticism amongst those of us who hold "traditional" assets regarding BTC.
As someone who holds real estate as part of the investment portfolio, I understand and see the return from the rental properties. Stocks give me dividends. Bonds give me interest payments.
Currently, all these yields are in dollars. But would I gladly accept BTC as payment? Currently -- no. It's too volatile for it to be useful. And the entire issue of blockchain transaction backlog is worrisome.
So if a tenant comes to me and says, "I'll pay this month's rent in BTC," I'd still have to say, "No thanks. I'll take dollars please."