I realised I didnt answer the question as to why there. It is worth pointing out, while I understand it may not make sense to yourself, it is indeed how much of the web works in relation to notifications. For example if you go to facebook and click a notification, it takes you there in the same tab. Same with twitter, linked in, monday.com and many other services I can think of. So it's likely (I am not one of the designers so can't say for certain) this is simply following that standard pattern. This is not to say you are wrong of course. I completely get your reasoning.