Labour's vote share was comparable to previous elections
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 Conservatives offered a streamlined, bare-bones manifesto that increased spending in key areas of voter interest (including healthcare, schools and crime) without promising the world. 
In the past, Conservative manifestos ignored working-class voter priorities. The NHS was often overlooked, with the logic of the day presuming that to engage with voters on the NHS would only draw attention to an issue that was a particular strength of the Labour party. In 2019, the Tories changed tact. They identified the key issues that resonated with voters and produced a laser-focused manifesto that promised to increase spending on the NHS and increase the minimum wage. This thin but poignant manifesto was sufficient to win over working-class voters. In addition to winning new voters, the manifesto was intelligently designed to maintain the Tory’s core voter base. The pledge of no increases to income tax resonated with more prosperous Tory voters, delivering a manifesto that offered something for both key demographics.
In offering a very short and limited manifesto, the UK Conservative Party was essentially saying it sees nothing wrong with the status quo. It indicates a belief that the country is fine as it is it. This is an affront to working people who grapple with stagnant wages, long NHS wait times, and inadequate poverty relief mechanisms.  Calling the limited Conservative manifesto a strength overlooks the extent that the British public is disgruntled with the way things are and their appetite for change (as indicated by the 2016 referendum result). The Conservative party won despite their meagre policy offerings. They got the party’s stance on Brexit right and were given a boost by a weak and divided Labour leadership. Their manifesto was more of a vulnerability than a strength.
[P1] Tory policies were laser-focused to target the key demographics. [P2] By not trying to promise the world or win everyone over, the Conservatives were able to win the votes that mattered most in key districts. [P3] This won them the 2019 election.
[Rejecting P2] By offering little in the way of policy, Conservatives were essentially saying they were happy with the status quo. This would not have resonated with the working class. [Rejecting P3] The Conservatives won because they got one thing right: Brexit. They won despite the manifesto, not because of it.