You have to add the "Content Following Item Updated Event Receiver" event receiver to the pages library.
Farm Solution with Feature and Module:
<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">
<Receivers ListTemplateId="850">
<Receiver>
<Name>Content Following Item Updated Event Receiver 850</Name>
<Type>ItemUpdated</Type>
<Assembly>Microsoft.Office.Server.UserProfiles, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c</Assembly>
<Class>Microsoft.Office.Server.UserProfiles.ContentFollowingItemEventReceiver</Class>
</Receiver>
</Receivers>
</Elements>
Or PowerShell:
Add-PSSnapin Microsoft.SharePoint.PowerShell –erroraction SilentlyContinue
$web = Get-SPWeb -Identity URL
$pagesListId = [Microsoft.SharePoint.Publishing.PublishingWeb]::GetPagesListId($web)
$pagesList = $web.Lists[$pagesListId]
$eventReceiver = $pagesList.EventReceivers.Add()
$eventReceiver.Name = "Content Following Item Updated Event Receiver 850"
$eventReceiver.Type = [Microsoft.SharePoint.SPEventReceiverType]::ItemUpdated
$eventReceiver.Assembly = "Microsoft.Office.Server.UserProfiles, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"
$eventReceiver.Class = "Microsoft.Office.Server.UserProfiles.ContentFollowingItemEventReceiver"
$eventReceiver.Update()
$web.Dispose()