What's stopping other CRM's from taking over Salesforce?

I've been working for a CRM company for the last 10 years, here are my 2 cents.

1. Salesforce isn't as dominant on the market as it seems. They don't even have 50% of the market.
2. Their direct competition is much worse. Dynamics, Oracle, SugarCRM — all of them look even worse.
3. CRM isn't a one-size-fits-all solution. Distribution and support are crucial for enterprise software and Salesforce along with others mentioned above are definitely A-players in this. They all recruit a network of worldwide partners, developers, and agencies ready to customize solutions. Only Dynamics can compete with Salesforce here.
4. There are many niches where Salesforce isn't number 1. Especially, in the mid and small-business segments. There are 500+ active CRMs who all keep the lights up.
5. There will be more successful CRMs in the future. My prediction is that the ultimate winner will be something like today's WordPress, where you have the main use case solved well and there are many extensions allowing to tailor CRM to the company's needs. Salesforce is kinda like that today, but it's overly complicated and it costs tens of thousands of dollars to make those customizations.