They get round GDPR by exercising the clause that talks about "legitimate interest"
Yes, that seems to be their technically-legal workaround with cookies as well. You tell them you don't want them to spy on you, but they use the excuse that they managed to spy on you before without your noticing - and you didn't object then - so you're a terrible rotter to go back on your word now.
All of them, but Amazon are among the worst. You buy a camera then they spam you with adverts of not only camera accessories (which you might need) but other cameras. Jeeze. How many cameras does one person need? I have 4 but only 2 in use at present. I dont need any more cameras at the mo thank you.
They keep trying to sign me up to that thing they've started whereby you allow them to sit on your shoulder all the time you're online and they constantly try to link what you're doing to something they sell and then try to get you to buy it. They think it will increase their sales, so what could be the problem? I genuinely don't think some of these companies realise/care that their sales numbers have an actual person with agency at the end of each one. They seem to think I'm like Michael Jackson in that documentary where he goes into the shop selling expensive gaudy items, the shopkeeper keeps pointing to things and saying "this is nice" trust me, it isn't and Michael says "OK, I'll have that, then" whilst you can literally see the shopkeeper rubbing his hands together.
eBay are similarly annoying when they email you to tell you what you've been looking at. I know: I was looking at it.... Especially annoying when I order something from them and then they email me soon afterwards to urge me to buy the same item. "Do you remember you looked at this?" "Yes - do you remember that I bought it?" Nice to know my order was so valued, then. Even when you look at random expensive stuff, just out of idle curiosity, to see what hugely impractical items people are selling and how much they're going for. I looked at old red telephone boxes after seeing some at a museum and eBay was convinced that I must be sitting there with my finger on my PayPal, just waiting to spend £3K on something that will prevent me from parking on the drive 
All marketing emails have to have an unsubscribe button by law, so you can just click this if it annoys you so much. It's at the bottom of the email. Big names like Clark's, sports Direct etc will definitely have this or they would be breaking the law.
Stop moaning, click unsubscribe and get on with your life.
So I'm the unreasonable one for not repeatedly telling them to stop it, often to no avail, then? As has been said, they ignore the law; probably work out that it costs them less to pay the fine, in the unlikely event that they get caught. I wonder if they have some kind of workaround whereby they maintain lots of different mailing lists and add you again every time you buy something or express any interest - thus, if you've bought 10 items from them over the last decade, you'll have to unsubscribe 10 times before they finally stop. That way of looking at things reminds me of the old Britannia music club: 'all' you have to do is 'simply' tell them every single month that you don't want to buy the random cassette that they've decided to sell you, or otherwise it's treated like you've ordered it! I know it was technically in their T&Cs, but it was never an honourable way of running a business.
I have a business Outlook account for work and I've noticed that Microsoft are in on the act now, as well. They send at least one email every day, claiming to help you manage your emails, but in reality just making it harder to find the real emails in amongst all their spam. Plus loads of emails informing me of every tiny little protocol and feature change that they clearly think are fascinating and very important, but which 99.99% of recipients must surely not give the vaguest stuff about and ignore. Maybe buried in some of the emails are notifications about the additional spamming liberties they're about to take unless you tell them not to. All the while, they send actual genuine emails - from people in my contact list - to the spam folder. Every time, I mark them as 'not spam', but still every new one gets sent there.