A corporation's obligation is to generate shareholder value. Not user value, but value for the owners. This can be done a variety of ways but the two big ones are: generating profits and distributing those as dividends or raising the stock value. Technically the former doesn't require growth, but the later definitly does. VC funded companies are basically founded with the promise that the value of the stock will rise and that the VC can cash out its ownership eventually, either through a sale or an IPO.

Also, growth doesn't necessarily mean size, but it does imply long term increase in value for owners. If I buy stock in a company, I want to get richer for owning that stock and that means either the dividends need to be high enough to recoup my investment or the stock needs to rise in value, making me richer when I sell it (starting the cycle again). Both of those outcomes sort of imply some sort of growth over time. If I expect that time to be short, as one might with an internet company, I'd like that timeline accelerated so I get as much value as I can in as short a time as possible. That's what leads to moves like this.