Because someone inserted a provision in the final bill that is totally unworkable. Under Texas law a city council must post a notice of any meeting for seventy-two hours prior to the beginning of the session. That notice must contain some basic information about the topics to be discussed at the meeting. But, the point the authors of the legislation missed, is another provision of the Open Meetings Act that requires the notice to be available at all times during that seventy-two hours. It can be a criminal offense for the council to meet if that notice has not been posted for the requisite time.
Any action taken at the meeting is subject to challenge.
Further, they can not discuss any topics that are not on the notice. The current bill would require the same posting on the internet. That question was not answered in the bill. The Texas Supreme Court has ruled that the Open Meetings Act must be read literally. In that case I think the legislature may have actually halted webcasts of public meetings.