The negative impact on Marvell Technology's stock price is primarily due to the disappointing Q4 financial results and weaker than expected Q1 guidance, which typically lead to a loss of investor confidence and a decrease in stock price. Although the company announced a $3 billion buyback program, which can be positive as it often signals the company's belief in its own undervalued shares, the immediate reaction to poor earnings and guidance tends to have a stronger negative effect on the stock price in the short term.