DigiKey has been changing a lot lately, but I can sympathise with their position. They have to make their website work for (at least) two very different use cases, which I'm sure is difficult.
On the one hand, they're a distributor. If you know what you want to buy, you type in a part number, add it to your cart, checkout, get it the next day, awesome. IMO they excel at this part of their website. I can log on two minutes before the deadline for next-day shipping, order the parts I know I want, get them before 10am the next day, super easy.
On the other hand, most of my time actually spent on DigiKey is discovering parts. Like many other EE's I use DigiKey for finding the best components to use in a new product. Designing a website like this has a lot more intricacies than just a stright-forward distributor ecommerce website.
One thing to keep an open mind about, is that while DigiKey might work for you, and you don't want it to change, there are new EE's joining our profession and hobby every day. Every day (maybe even multiple times per hour?) there are people navigating to DigiKey for the very first time, placing their first ever order. This is the reason websites continually change. It's not just "change for the sake of change". As EE's we don't change all the parts on our BOM because we feel like it, but if we find a more efficient part, a cheaper part, or need to replace an EOL'd part, we will make the change because that's worth our time.
A good example of this is the recent picklist change, where the picklists went from normal html select lists, to the (imo) frustrating picklists that no longer perform like a normal html select list. Using CTRL and SHIFT to select multiple is items is broken now, and replaced by selecting individual items by clicking on them. This change is frustrating, but I understand why they did it. I've stood behind at least 3 junior EE's who while using digikey, would select one item from a picklist, view the results, then go back, select another, view those results. When I pointed out that they could select multiple items, they were surprised that this (basic, default html select) feature existed. I observed these same people trying to select multiple items by just clicking on them (like you can do now). This is why websites like DigiKey make these changes, because while you may know how to use the tool very efficiently, there's bound to be lots of people less experienced learning or struggling.
It's a tricky balance to keep. On the one hand you don't want to alienate your existing customers, but on the other hand you want to make it as easy as possible for new users to make their first order. Inevitably the balance usually tips more towards the new users, as experienced users are probably less likely to leave over UI changes. I know I won't leave over the new picklists. While I really don't like the new picklists, I know that the value DigiKey offers is in more than just their picklists.