The magic of web 2.0 were the open apis. Developers could use these apis to mashup services how they wanted. Sometimes these developer's tools and mashups became so popular that they would come to define the entire service of which they were building atop. Both hashtags and the term "tweet" originated outside of Twitter, Inc.
But when these services grew they morphed into platforms. Their apis were closed off and the developers that helped these companies find their success either kicked off or severely limited in what they could do. This became a pattern, not just with Twitter, but many services that found success in thanks part to their open api followed the same playbook.
Existing players making unpopular changes to their policies is usually a boon for the upstart. Each time this happens a vocal group of users becomes dissatisfied with the platform who then attempt to migrate to an alternative. However each migration causes some kind of loss. Data doesn't transfer or communities fracture because not everybody moves. Not to mention the energy that could have been spent doing something else.
Contrast this with something like email. You can email anyone you'd like, even if they don't use the same provider as you. If your mail provider changes a policy you don't like, you're free to change providers without losing your identity on the internet. People can still contact you the way they always had and you can still contact them. Your data can move from platform-to-platform seamlessly. There's nothing re-organizing or hiding emails from your inbox unless you setup the rules (or use gmail).
The difference in experience between twitter and email is night and day. One keeps you locked in and subject to their whims, while the other gives you the choice to use it however you see fit. The difference is that twitter is a platform and email is a protocol. Pick protocols.