Why are there so many vacant buildings near Parliament Hill?

A November 1, 2019 article:
     "While 19 of the 38 street level shops on Sparks Street's north side are either vacant or construction offices...archival photos show a a much different past. (CBC Ottawa, The heyday of Spark Streets north side.)

Blocks 1,2 and 3 are being redeveloped. The property outlined in blue is the Parliamentary Precinct.

Vacant.
90 Wellington.
100 Wellington
67 Sparks
93 Sparks
183 Sparks
185 Sparks
CIBC bank - 119 Sparks
179 Sparks
Buildings on the Mall that were privatized,
Thomas D'Arcy McGee - 90 Sparks.
The Parliamentary Precinct - Eroding Boundaries
Recent years have seen a return to the confusion and contested boundaries of the early 20th century. In the seventies, because of accommodation pressures on the Hill, Parliamentary activities were moved south of Wellington with the conversion of the Metropolitan Life Building (Wellington Building) for House of Commons use. This blurring of boundaries and the confusion about the relationship of the Parliamentary Precinct to the city continued with the purchase and lease of additional space for Parliamentary use south of Wellington Street.
At the same time, the approach to departmental accommodation became less controlled. Once again, private sector interests began to put up speculative high rise developments which were then leased to the government. The only major government initiative during this period was the construction of large offices complexes in Hull.
In 1973, the Department of Public Works expropriated all the land south of Parliament Hill, between Wellington and Sparks Streets. The intent was to create a "South Block" which would provide Parliamentarians with permanent accommodation south of Wellington Street..It is understandable that Canadians and Parliamentarians would want a comprehensive approach to preserving the Parliamentary Precinct...The possibility of extending the Parliamentary Precinct west from Bank Street to Kent Street is being explored. (Google: Foundation-Building the Future - House of Commons.)
The Confederation Square National Historic Site of Canada encompasses the Bell Building, Central Chambers, Chateau Laurier Hotel, Langevin Block, National Arts Centre, Ottawa Postal Station B, Scottish-Ontario Chamber and Union Station.
Confederation Square was established in 1939 and is the second most important ceremonial centre in Ottawa, after Parliament Hill.
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Public Works is only offering short-term leases on the Mall according to the November 1, 2019 CBC article "Sparks Street great divide bad for business."