It's not really due to environmental reasons. What happened is these big refillable bottles that will replace small toiletries are more cost effective for hotels. However, the problem has always been that guests thought of these as a less premium offering (thus you would only find them in HIX etc). Now that public perception is changing and the environment is a concern for guests, IHG grabbed the opportunity to save some cost.
Spot on, however a hotel/resort can package/present the toiletries to make it look/feel not less premium. The newly opened Waldorf Astoria Maldives, where rooms start at $1,500 per night, for example utilise large dispenser bottles but obviously with higher end brand content - it felt very premium. On the other end of the spectrum, I can understand how a plastic dispenser stuck on the wall will feel cheap no matter what product is inside.