Liberal Tories deny the death of the establishment

If we assume that the Tories do not get tactical anti-Labour support (as the Tories tend to claim) then their relative popularity is explained by them being the accepted party of the establishment... such that a non-socialist voter would unquestioningly support the Tories despite there being other parties with similar policies. It is this loyalty to the Tory party by the voter which is due to them being the party of the establishment which makes the Tory party such a potent threat to Labour.

But over time this loyalty to the Tory party being the party of the establishment on the right will erode and voters will be prepared to let the Tories lose even if this means letting Labour in. It is not enough for the party of the right to rely on voters being loyal to their monolithic establishment party because eventually voters will resent being coerced into voting for a single party. They will resent their vote being taken for granted and they will let Labour (the Democrats in the USA) win.

The establishment on the right is dying which means that people support parties other than the Tories and this means that the first-past-the-post system is a problem for liberals. If the establishment is not dying then fptp doesn't disadvantage liberals but otherwise fptp is helpful to the left. For Tories to continue to support fptp means that either they do not care about losing to Labour (they are not liberals) or they are in denial with regard to the death of the establishment. Liberal Tories who support fptp are in denial of the death of the establishment.