After 20+ years, certifications in Microsoft and Cisco platforms, and 12+ years inside Cisco Systems, I am of this opinion:
Freely making available study blueprints (for exams), study guides (guided topical self-training books/downloads), and freely-available virtual appliance VMs (OVA, etc.), could in no way be deemed detrimental to the vendor's market share or bottom line - in fact just the inverse. The key is making the exams tough enough to weed out the 'players' from the 'stayers' - those who truly learned the content and who can think their way through scenario-based exam questions. This puts most of the onus on the exam development team: want good practitioners... write well-crafted (eg., not vague and grammar-splitting idiotic) exam questions / scenarios.
Beyond that, requiring that same training content be restricted to a paid-course with a talking head (or even a very skilled practitioner) guiding the discussion in a group setting - simply amounts to the vendor seeking another revenue stream. This is short-sighted. It's also not always effective in many cases with a 10:1 or 15:1 student-instructor ratio.
From a business perspective, the vendor will more than offset the cost of developing the training content, through increased sales, and delivering more certified professionals who are capable of recommending (consulting) or implementing (technical bench) the vendor's products.
The fact is that training platforms like Pluralsight (one of the best platforms visually / structure / content) / Skillsoft (skillport.com) / Safari (not my favorite), provide advocate / enthusiast-produced content in a professional 'learning management system' (LMS) platform, allowing tracking of progress, achieving milestones, and even facilitating exam prep and possibly integration with vendors like PearsonVUE, etc. to schedule exams.
Cisco has done this with their 'learningnetwork' system - but again at an exorbitant price point for the content.
Whether detailed study guide content is available or not - exam blueprints/guides should be available - providing the outline of what you need to study. Then I suggest the following approach for networking / technology studies:
1 - Get a newer or even a little older PC and load it with as much RAM as it can take (minimum 16GB, 32GB or more preferred) (CPU is not as critical here for non-production use)
2 - Install EVE-NG as your virtual lab platform (FREE) (can also use GNS3 in many cases)
3 - Get VMs and software images whatever legal means you may do so (Cisco .bin OS images, CP FW VM - available for download, Arista EOS VM, etc. - whatever you might want to study) (FREE)
4 - Build template machine images in EVE, to be reused across various lab scenarios
5 - Practice these scenarios
The last item can be influenced / guided via content in places like this forum, StackExchange, etc. where exam content is discussed.
In closing - it seems self-defeating to arbitrarily limit training to classroom-based (instructor led training (ILT)) or even virtual-instructor-led training (V-ILT) - which is usually the same price as in-class pricing - though you'd save on the travel costs.
Business development 101:
Make the best / most effective / easiest to manage products ==> Then grow vendor-skilled consultants and tech practitioners = grow support for that vendor across industries and the world = market readiness-to-execute = market penetration = happy customers.... rinse and repeat.
Cheers!