Here are the results at the Wiki article for “2016 Washington, DC statehood referendum.” Google for more info.
Advisory Referendum B
Choice Votes %
Referendum passed Yes 244,134 85.69
No 40,779 14.31
Valid votes 284,913 91.59
Invalid or blank votes 26,154 8.41
Total votes 311,067 100.00
Registered voters & turnout 478,688 64.98
Source: [22]
As you can see comparing DC’s 2016 with PRs 2017 turnout of 23%, DC had almost 65% turnout—massively higher. Of that 85.69% voted yes. Thus 51% of all registered voters in DC favored the constitution statehood referendum. So statehood had more than double the support of DC voters compared with Puerto Rico.
Turnout figures are not give for PR in 1998 and 2012, so no comparison can be made.
There are other issues as well, such as the fact that DC is a city with a very small land area. The land of the District of Columbia was contributed by the state of Maryland.
The state of Virginia had also contributed land to form the District of Columbia. But that land was eventually given back to Virginia. Statehood rights, voting rights, etc could be achieved by giving back the remaining area of the District of Columbia to Maryland.