I understand not every company does this and I get that companies want to keep their brand integrity in check, however it seems to backfire when they make it so difficult to access said guidelines designers tend to make up designs and thus fall out of brand, especially in rush jobs. I also understand that a designer can request access, but they seem take so long to respond – if at all. It just seems so pointless to keep everything under wraps.
I work in the trade show industry so I create sponsorship signs for a variety of shows. Most of the time I am supplied graphics from a show manager but sometimes I am required to ask for the logos directly from the companies. My answer is geared towards asking for a logo but can apply for branding guidelines as well.
There may be a couple of reasons why.
1) They do not have branding guidelines. Depending on how big a company is, it is very possible they do not have branding guidelines.
2) The people you contact have no idea what you're asking for. If I mention I need a logo in vector format: EPS, AI or PDF. It is a 50/50 if they know what I mean. I have been given so many raster logos in an eps file.
I would also like to know how you're asking these companies for their branding guidelines. Are you expecting to find these details on their website? Are you emailing an info email address? When you do email the company for their branding guidelines, how are you asking?
but they seem take so long to respond – if at all
Very dependent on the employee you're in contact with. This isn't anything you can really do besides pressing the issue that the graphic service is close to a deadline or try to speak with the right employee at that company.
So I would argue that it isn't always a company trying to keep their branding guidelines under wraps, you're just dealing with a company who doesn't have branding guidelines or you're speaking with people who are unsure of what you're asking for or an employee who is slow to respond to emails.
Also it is common for me to ask clients for the correct logo multiple times. Whether that is for a high-res version or something that isn't corrupted...
You're often dealing with business people, many who may not really know anything about design and branding. They may also be quite busy with other projects and business needs. Locating and sending out brand guidelines to an outside party might not be a high priority for them. The same issues can also impact in-house designers - a lot of the issue just revolves around busy humans with different personal and work priorities. If the business has a marketing team, try and work through them as they'll likely have more experience and understanding of what you're asking for and why.