There are a few main reasons behind the problem with online reviews.
It is easier to choose a differentiated product as consumers will more likely to deduce if that will fit their needs. But less so when there are many similar products (like cereals) for which people will need a mental shortcut, e.g. random choice from a physical grocery shelf or reviews from an online marketplace. More personalized recommendation might help but it will not work for homogeneous products.
It is harder to evaluate a product virtually than physically, particularly so for stuff like clothing for which the sense of touch or smell is important. The advances of mixed reality technology may help reduce this gap, but it remains wide so far.
