As PP have said, they all get sent freebies and sponsorship for mentioning certain brands and most successful bloggers rely on this to keep the blog updated and to keep their readers buying stuff that they get commission on for posting about.
I got into fashion blogs aged about 11 or 12 and have watched some of my favourite bloggers change beyond recognition as they gained popularity, going from a few hundred followers to hundreds of thousands. At first they were wearing high street and vintage that was accessible and individual, now they are all identical in expensive looks head to toe and with ludicrously expensive handbags that every other blogger at the same level has, obviously gifted as otherwise why would these 'trend setters' want something everyone else seemingly has. It's boring and I no longer enjoy reading their blogs as I get nothing from it now, I'm not going to pay £300 for jeans that you recommend because you got them for free. If I see another Gucci Dionysus bag, JE Anderson nose ring bag or double g belt or Chanel espadrilles I might vomit. It's disingenuous, one claimed she would never buy an 'it bag' and now has a different one slung over her arm every post, alternating with overpriced basket bags to make it more 'real'.
It changes the blog totally from what people liked about them in the first place, one blogger I liked now goes on holiday several times a month so her old posts on London street style that would be wearable for most have all but disappeared in favour of posts documenting her extensive 5* holidays and the bikinis she has spent the best part of £1k on (or more likely been given for free and not disclosing this fact) Its not relatable and not even aspirational anymore as only a blogger or a trustafarian could live that lifestyle and it seems so shallow and pleasure driven. Don't get me started on the ones with eco credentials who are flying all over the world on a regular basis...
A lot of the mummy bloggers obviously have wealthy husbands that fund their shopping and it is all they do, constant story updates on Instagram in changing rooms and opening boxes that have been delivered. Again very boring. They tend to make sponsored posts more obvious though, I know they are obliged to say now if a post is sponsored by a brand but I think there are ways of getting around it if the item being promoted was 'gifted' rather than the blogger being paid a lump sum for a post.
It's a huge money maker for the bloggers but it's such a shame that they go from genuinely recommending products they have bought and tried themselves to hawking whatever brand will pay them well to do it.