Remember when ebay just used to match up the keywords you searched for with listing title keywords and just showed amazing results that were logically relevant?
You can avoid "streamlining" when searching by avoiding the Price plus Shipping: lowest first sort order.
You can avoid keyword substitution and automatic category navigation in your searches by putting a keyword in quotes to force eBay to return only literal keyword matches.
Other than sponsored listings appearing in the results -- which for a time could be filtered out using an ad blocker -- and keywords being matched to item-specifics instead of just titles, it is still possible to get search results that are quite similar to those results obtainable prior to the adoption of Cassini.
There are some other differences: inability to uniquely search certain punctuation characters, and the lack of wildcard characters. The old pre-Cassini search had an interesting way to find results that had any combination of m number of keywords out of a list of n keywords, while the current search interface more easily allows a simple Boolean OR search among a list of keywords.
Some of the current limitations of keyword matching can be offset by using filter options, which encourage sellers to conform to certain standards in the listing format through limited item-specific options. Try searching for pipe or hose by fractional measure of inner diameter, outer diameter or wall thickness to see a limitation of current keyword matching and the benefit of using filter options.
Why do they refuse to just show buyers what they search for?
eBay would rather show buyers a few things that eBay thinks they are likely to purchase, rather than including all the results that actually meet their search criteria that those buyers are (in eBay's self-interested estimation) probably not really interested in buying.
Those users that insist on logically-consistent and complete results can still get those, too; just not by default without using techniques like those described above.
