Telco practically can't deliver OTT

Do Telco can provide OTT service? Most of them can’t. Not because they technically not capable, even their capability block them to deliver OTT service.  Why is that ?

This is the answer, summary of the article from wikipedia 

The term OTT or "over-the-top" refers to the delivery of content or services over an infrastructure that is not under the administrative control of the content or service provider. Originally it referred to the delivery of audio and video content, but more recently the definition has been extended to include any service or content and in a more general sense means any service available on the Internet.

Recently, over-the-top is wrongly used in the telecom world to describe any unmanaged service delivered over IP. If an operator offers an IP service (say IPTV), and that service is delivered over the operator's infrastructure (whether mobile, fixed, or otherwise), it is not OTT. If that same operator, after building a content/service model, extends the service to any IP end point on another operator's network, then it becomes OTT. Whether the operator decides to use QoS for the service is irrelevant in the definition of OTT. In other words, an operator offering a service to its own subscribers is never OTT; rather if quality and bandwidth are enforced, it is a managed telco service, and if not, it is an unmanaged telco service. Only if it is extended beyond the boundaries of that telco's infrastructure is it ever correctly referred to as OTT.