i'm not entirely sure that's the case - the tories were (before brexit and covid overtook just about everything else) talking about changing constituencies (as they said) to even the number of voters in each constituency, and the general consensus said this would advantage the tories. obviously how you draw the boundaries, and how enthusiastically you try to get people to register, will also have an effect.
as
redsquirrel has said, it's quite rare in the UK for one party to get more votes but less seats than the other.
while FPTP has its flaws, i'm not sure the idea of a UK-wide party list - which seems to be what you're advocating - appeals.
it would pretty much remove all remaining influence of local political party members to select candidates, and take away any link between MP and constituents, and MPs would serve their party HQ first and the electors second.
while personally i currently live in one of the safest tory seats, so i've never really seen the point of writing to my MP about anything, i think a lot of people would want to keep that option, rather than just have a bunch of party place-people selected by london based party HQ as lobby fodder.
and would remove the opportunity for any independent to stand on local issues (it doesn't often happen that they are elected, but think it's important they can - was it kidderminster that last did it?)
had this system been brought in, i'm fairly sure that any remotely left wing labour MPs would have rapidly ended up fairly near the bottom of the party list...