It's quite simple, actually: a customer needed a very large database (> 4G) and one proposal was to create some kind of sharding mechanism because all of the ways that they could think of to do this in RAM meant that they had to use a pretty large number of machines, complicating all of the ways in which updates, queries and keeping it all synchronized would have to be done, besides requiring a rack full of hardware.

The Alpha made all of that moot because in one fell stroke it increased the amount of RAM that could be addressed directly to the point where the whole thing could happen in memory without any cluster communications overhead. It was still an expensive machine but it cost a fraction of the setup that it replaced, and performed really very well. A nice example of how vertical scaling can be a very viable option. The 64 bit file system also allowed for much larger files, which helped the project in different ways.

One downside was that spare hardware was difficult to obtain but the system was built like a tank and ran for many years until there were many other suppliers of 64 bit systems.

It was way ahead of the anything else in the 'affordable' range of computers. Though it still cost as much as a nice car fully decked out, especially the RAM was quite expensive.