1. In the last decade, the politics have definitely shifted to being more anti-immigration than they used to be. For example, it takes at least 6 years to qualify for UK citizenship. This is 5 years to qualify to ILR (Indefinite Leave to Remain) and a year of ILR to qualify for citizenship. This used to be 4 years to get ILR (prior to ~2006?).
2. Adding of extra requirements like Living in the UK test and a nebulous "good character" test.
3. Uncertainty over Brexit. It's far from clear what UK citizenship will get you post-Brexit, if Brexit even happens. Given the rise of the Brexit party and the Tories tearing themselves apart with May resigning and a hard Brexiteer like Boris Johnson likely to be the next PM, a hard Brexit has become much more likely. This may also negatively impact the UK economy.