Hey Israel,
Great question! I wouldn't say there's one overly-common excuse I hear regarding adopting a more pattern-driven process. In fact, most companies and teams are on board with the basic principles of modular design. After all, there are a ton of benefits of this style of design and development (atomicdesign.bradfrost.com/chapter-4). Sometimes I encounter skeptical teams who think they don't need to invest in a design system, but conducting an interface inventory (atomicdesign.bradfrost.com/chapter-4) with them usually sorts that right out!
It's one thing to say you're on board with modular design, but it's a whole other thing to make it a cornerstone of your process and workflow. I'd say the biggest hurdle I see companies face is entrenched processes and workflows. It takes a lot of effort to change your existing processes, and it's super easy to fall back into old habits.
A hugely fulfilling part of my job as a consultant is to work with companies to help adopt a more pattern-driven, collaborative workflow. That involves coaching them, leading by example, and letting them know when they're reverting back into old bad habits.