I am not giving the tabloids credibility because they don't back up anything they say; nor do they put their sources on the record by naming them. The reporting is rampant and if a lie is repeated often enough it is taken as truth.
The purpose of not revealing their sources is quite simple. The source would be sacked and so they would lose their source.
The fact that there are so many reports either means that there are multiple sources, one source revealing stuff to multiple outlets or there is nothing in it but to simply refuse to accept that the tabloids may actually have real sources because they don't name them it to ignore the consequences for any such sources should they be revealed - lose of job - and the consequences for the outlet - loss of a source.
In addition, in the UK, journalists are expected to protect their sources by not revealing them unless the court rules it is in the public interest for such sources to be revealed.
Not naming a source doesn't mean there isn't a source but that the journalist is actually protecting their source as they are entitled to do by law - Contempt of Court Act 1981 (in the UK).
More on the rights to protect sources
https://www.inbrief.co.uk/media-law/journalists-sources/
Thus anyone who simply ignores a story because of unnamed sources really is ignoring British law and the rights of British journalists.
This is becoming increasingly bizarre.
Edited to add: I made myself read the entire MoS article, something I almost never do and really, "bizarre" sums it up perfectly. The writer(s) throw everything--and I do mean "everything"-- but the kitchen sink out there. They are alternately fawning, critical, and filled with faux concern. Harry's changed and it's clearly implied that it's Meghan's fault, although it started when William expressed brotherly concern on the speed of Meghan and Harry's relationship..Kate is called the "Steel Marshmallow"(?!). It's implied that there are leaks from the staff at Anmer, from within KP, and from Kate and William's friend group. Charles had to smooth things over, Meghan is consistently rude and pushy, especially to servants, and so on. Everything but the kitchen sink, and for any of this to be true, the MoS must have had microphones in every home that the royal family own.
My mind, it is boggled.
They don't need microphones - just multiple sources.
Given the salary of the palace employees there are many who will supplement their wages by leaking what they hear around the palaces to the media - often mundane stuff but often very good and reliable scandals are leaked via this route.
We know from past history sometimes the leak is from a royal themselves (Diana and the Morton book), highly placed staff but mostly it is from the lower ranks within the household.
There are 100s of people working in the royal households so 100s of potential sources for the media - some are even told by the royals to leak stuff and then in the official leak will come something not authorised which sets up a media buzz to find out more and then more and more staff are approached until the media gets a story.
With the number of stories there is something going on - a leak and it could be from a staffer or it could be from a friend within their circle who has been hurt. It could even be from within the family for some reason.