"Enterprise" slack is $15 per head per month. This would equate to an recurring annual expenditure of nearly $4.86million for Uber's 27000 employees.
Given that Slack can be seen as IRC with some pretty decoration glued up to an Elasticsearch instance, and that Uber already has a highly trained tech org in place, if it wants to make a Slack "clone" for less than, say, $25million (cost of Slack to Uber for 5 years), it could actually be a pretty sensible decision- especially when you take into account the tax and stock-price benefits of capital expenditure.
Given that Slack can be seen as IRC with some pretty decoration glued up to an Elasticsearch instance, and that Uber already has a highly trained tech org in place, if it wants to make a Slack "clone" for less than, say, $25million (cost of Slack to Uber for 5 years), it could actually be a pretty sensible decision- especially when you take into account the tax and stock-price benefits of capital expenditure.