...but companies like Intel, AMD, NVIDIA and Microsoft do share roadmaps of key products (if only to big customers, OEMs and dealers who sign NDAs -it filters down) so people have a reasonable idea of where the PC platform (hardware and software) is going.
The issue is with Apple is that they control all the key components of the hardware and software and can pivot on a dime without any notice. Its maybe not such a big deal for more consumer-focussed products like the MBA or lower-end MBP, but I think there is a particular problem with the pro desktops where they have a dreadful track record of releasing one-and-done products like the trashcan, iMac Pro and 2019 Mac Pro, leaving them to go out of date then going off in some radically different direction with the "successor" that won't necessarily support the same workflow. If you have to spend a year planning/budgeting/writing proposals for a large project that will run for several years, it's rather useful to know that the equipment that you specify in the proposal will still be available in some recognisable form 3 years later if you need replacements or additional seats. Even Apple's position on end-of-life for MacOS versions seems to be a case of guessing based on past performance. E.g. although we know that Tahoe will be the last Intel-compatible MacOS we have to just assume that it will get 3 years support - and nobody really has a clue if there will still be a PCIe Mac Pro this time next year. It would be a very "courageous" move to plan an important project that assumed there will be a drop-in replacement for the current Mac Pro or Studio Ultra for the next 3-4 years.
There's also some debate as to whether the Osborne Effect really happened (even on the Wikipedia page there's a lot more to that story than 'announced the replacement - killed sales'). Meanwhile, Apple are somewhat unusual in how they rarely announce products unless they are either available on day one or have a firm, near-future launch date (the exception being the 2017 Mac Pro crisis where there was obviously blood on the carpet). For the rest of the industry, it's fairly typical for new products to be teased at trade shows and/or not show up for sale for months after they are announced).
Apple doesn't need to make an announcement for people to assume that the M5 MBP announced in October means that M5 Airs and M5 Pro/Max MBPs definitely probably might be coming soon - and even people who don't scour the interwebs for rumors are going to ask why the cheaper MBP is "M5" while the more expensive one is only "M4" - so some "Osbourning" will be happening anyway. I guess Apple are pretty confident that people who delay buying will hold onto their money and not be tempted to spend it on anything else in the meantime...