I have implemented publish/subscribe middleware in the 90s using UDP and reliable IP multicast. It was not too hard to do and had taken me about two month. Yes I did reinvent the wheel but it had numerous positive sides:

  a) It added yet another area of expertise to my portfolio.
  b) I did it because it was needed to facilitate another product in the company where I worked. The alternative at the time would be paying $350,000 for middleware from Vendor-X. Not acceptable.
  c) Vendor-X people noticed us, loved what we did and made us a partner to resell their middleware and we've made a ton of money on deployment, configuring and consulting services.