When zoomed out, you are seeing a buffer containing a quick-and-dirty decode of your RAW. Some effects can work on this sort of data. Some effects rely on the RAW data by way of the particular algorithms used, so the only way to visualize the effect is to view the image at 100%. 100% is wysiwyg, zoomed-out is not. To change this, a developer would have to choose an alternative algorithm for those effects which may only be visualized at the wysiwyg 100%. In the end, what you get in the output is an entirely different process by which all the effects are lined up in a certain order, the toolchain pipeline. From the documentation, “Everything that happens to an image, from the moment you open the file to the moment it is displayed on screen or saved, takes place in a fixed order. The data flows from one module to another - this is the toolchain pipeline. RawTherapee contains four pipelines (one for the main preview, one for the saved image, one for the thumbnail, and one other that currently escaped me).” http://rawpedia.rawtherapee.com/Toolchain_Pipeline
So, when your main preview is zoomed out, the pipeline skips the algorithms which work on the RAW data, and you see only effects which are compatible with the preview buffer’s data. Although computers are a tad faster than they were in the bad-ole-days, this feature allows many effects to be adjusted quickly without being bogged down without including the processing-time overhead that would be required if every RAW-dependent algorithm were to be included. At 100% there is a more finite subset of data in the preview, and the pipeline will include those algorithms.
Toolchain development experts like @heckflosse, @agriggio and others might be able to revise and extend these remarks for you. Welcome to the forum!