There is a limit on maximum number of Push Topics(PushTopic) records per org in Salesforce.
For Performance and Unlimited Editions: 100
For Enterprise Edition: 50
For All other supported Editions: 40

 

SELECT Id, Name, CreatedDate, CreatedBy.Name FROM PushTopic WHERE IsActive = true

If you want to  increase in the number of delivered event notifications within a 24-hour period, contact Salesforce Support for help.