Article: Groove recordings, first designed in the final quarter of the 19th century, held a predominant position for nearly a century—withstanding competition from reel-to-reel tape, the 8-track cartridge, and the compact cassette. In 1988, the compact disc surpassed the gramophone record in unit sales. Vinyl records experienced a sudden decline in popularity between 1988 and 1991, when the major label distributors restricted their return policies, which retailers had been relying on to maintain and swap out stocks of relatively unpopular titles. First the distributors began charging retailers more for new product if they returned unsold vinyl, and then they stopped providing any credit at all for returns. Retailers, fearing they would be stuck with anything they ordered, only ordered proven, popular titles that they knew would sell, and devoted more shelf space to CDs and cassettes. Record companies also deleted many vinyl titles from production and distribution, further undermining the availability of the format and leading to the closure of pressing plants. This rapid decline in the availability of records accelerated the format's decline in popularity, and is seen by some as a deliberate ploy to make consumers switch to CDs, which were more profitable for the record companies.

Now answer this question: What was a major cause of declined vinyl sales?
major label distributors restricted their return policies