I’m not sure that’s an accurate or defensible perspective on why they failed. From Wikipedia:

Pets.com lacked a workable business plan and lost money on nearly every sale because, even before the cost of advertising, it was selling merchandise for approximately one-third the price it paid to obtain the products.[22] Pets.com tried to build a customer base by offering discounts and free shipping, but it was impossible to turn a profit while absorbing the costs of shipping for heavy bags of cat litter and cans of pet food within a business field whose conventional profit margins are only two to four percent.[22][23] The company hoped to shift customers into higher-margin purchases, but customer purchasing patterns failed to change and during its second fiscal year the company continued to sell merchandise for approximately 27% less than cost, so the dramatic rise in sales during Pets.com’s second fiscal year only hastened the firm’s demise.[22]