This objection is manifold but in simple terms, is founded on the philosophic problem of predetermination. The following quote is also found in the aforementioned BLS research paper. If a fixed weight formula, such as the Laspeyres, is used for the index, relative prices of items are compared with respect to a fixed market basket of goods and services. In either case, it is assumed that the spectrum of products, and the available attributes of the goods or services from which the consumer may choose are the same in both the reference and comparison periods. In practice, however, the specific items on the market are often changing.
Models disappear and new, different ones appear to take their shelf space.
Sometimes the differences between old and new models are minor, or are regarded as such by the consumer. Sometimes qualitative changes can occur which make the new products difficult to compare to the old ones. These physical changes in consumer products and services can be observed, but their value to the consumer must be excluded from a consumer price index measure. I call the reader's attention to the reported assumption of a fixed weight formula, namely that the products available to consumers will be the same. My read of this assumption is different.