Becauae making a good product is not their goal, and never was.

MS exists to monetize their products, or in other words extract maximum profit. When they were an underdog or compwtitor (Win 3.1 era), making a better product was the primary way to beat Apple et al.

But now they rely in integration/lock-in of their ecosystem, and making their products better will not increase their market share. That means improving their products is against their financial interests.