Many governments worldwide have laws enforcing them to publish their expenses, contracts, decisions, and so forth, on the web. This is so the general public can monitor what their representatives are doing on their behalf.
Update: With the release of the Panama Papers, a reliable means of exposing corruption and the methods of money laundering and tax evasion are now even more important. Web scraping provides an avenue to find, collate, and organize data without relying on information leaks.