A streamlined manifesto
The Tory manifesto was more streamlined to cater to key voter interests.
In many areas that Labour lost to the Conservatives, their vote tallies were similar to previous elections in which they had won the seats.
The vote tallies indicate that Labour didn’t unravel. Their vote share in many of the areas they ended up losing to the Conservatives was comparable to previous Labour showings in 2001 and 1997. The Tories were simply able to surge and pick up the seats. The Conservatives took 44% of the national vote, their highest vote share since 1979. This strong performance indicates that it wasn’t so much a Labour collapse that handed the Tories victory, but a Conservative surge. 
The Darlington constituency serves as good illustration of what took place across the North. Ther, the Labour candidate garnered 17,607 votes, about the same as they did in 2015 and more than they secured in 2010. The Conservatives won the seat with over 20,000 votes, indicating a slightly better showing than they managed in 2017.  The same narrative played out across the country, including in key seats like the Vale of Clwyd, Stockton South, Bishop Auckland and Bolton North East. In 2005, Tony Blair won a majority with 35.2% of the vote. In 2010, Gordon Brown earned his majority with 29% of the vote. In 2019, Labour won 32.2% of the vote, putting up a fairly strong showing. But the Conservatives were just able to do better. The defeat didn’t come from a collapse of Labour voters, but a particularly strong showing from the Conservatives. 
The Conservative party was in disarray. Boris Johnson was hiding from journalists in fridges, lying in every other sentence, dodging interviews, and stealing phones to avoid difficult questions. To say the Conservative Party was on sound footing for the 2019 general election is grossly overstating the strengths of the Conservative Party. The Conservative Party also didn’t perform particularly well at the ballot box. Despite earning an 80-seat majority, it was only able to increase its share of the vote by 1%. Labour’s, on the other hand, fell by 8%.  This clearly suggests that the Labour party’s failings were the main factor behind their election loss, not the Conservative party’s relative strength.
[P1] The Labour vote share in many constituencies was comparable, if not stronger than previous elections. [P2] The Tories just performed far better than in previous elections. [P3] Therefore, it wasn't Labour's unravelling that cost them the elections, but a strong Tory showing.
[P1] The Conservative's election campaign was appalling. [P2] They also didn't vastly increase their vote tally. [P3] Therefore, the election was not won on the Conservative Party's merit.