Quite early in the OSM project (2007), the free road data from the US Government (aka TIGER) was imported[0]. However the quality of the data was, in retrospect, poor. Even now, the data is of poor quality in the USA, especially compared to other develeped countries.[2]

It also makes the map "look done", and the USA, despite it's population size, doesn't have as active a community of mappers. The USA has about the sized OSM community as the UK or Germany, despite having 5 times the size.

One theory is that since the map for the USA "looked done", that people thought it was done, and hence didn't start mapping and that hindered the growth of the community there.

To see more, zoom in a lot in OSM in the UK or Germany, and compare similar sized towns/cities to the USA. The USA map will usually just have the roads (with names), whereas in the UK or Germany you'll find much more shops, schools, footpaths, carparks, parks etc. mapped.

[1] Details of the import http://wiki.openstreetmap.org/wiki/TIGER [2] A long time OSM mapper points out some of the problems in 2015 of the USA's data http://www.openstreetmap.org/user/Richard/diary/34290 Or this: http://www.openstreetmap.org/user/Richard/diary/26099

In general the OSM community errs on the side of vetoing new initiatives -- doing an import properly means raising it on the mailing lists, which invariably attracts vastly more criticism than assistance. Even coordinated (non-automated) remote mapping attracts considerable criticism these days -- most ludicrously, by people suggesting that it's better to leave an area unmapped so that it might one day attract local mappers (rather than remote contributors who will work on it immediately).

There's also the question of the license. Without opening a can of worms about the usefulness of sharealike provisions in general, I think it's safe to say that making a geocoding result trigger sharealike implications in a database is clearly problematic (consider geocoding a database of customer addresses, then being obliged to share the rest of the table!). Unfortunately OSM hasn't yet reached agreement on a geocoding guidance. Consequently a couple dozen of us working on OpenAddresses have gotten the project to over 200 million addresses in less than 2 years. OSM is now a decade old, has millions of registered mappers, and contains less than 60 million addresses.

I don't mean to be all doom and gloom, though. I would love to improve OSM as a home for address data. And I urge those of you who care about this incredibly important resource to join me -- hop on the talk and legal-talk lists and help make the case for a geocoding guidance that makes sense.