The depth of the PL has to be what's helping these clubs find the fight to come back like this. Tottenham and Liverpool have to navigate a competitive top six where your Juves, your Bayerns, and your Ajaxes have none or one main competitors basically in the league every year.
On top of that, I think the EPL has the most competitive mid-table. I don't think La Liga or the Bundesliga really have the collection of squads that can hurt you on any given day like the EPL does. Playing the Watfords and Leicesters and Wolves of the league also helps keep you competitive each week. I know there's that "Can he do it in Stoke on a rainy Tuesday" joke about how the English tend to pump up their mid-table teams too much, but it's actually true at this point, I think.
Liverpool and Tottenham were in a fight every week that they're not playing Huddersfield this year. Even Fulham pushed Liverpool at Craven Cottage a few weeks ago. EPL squads are blooded in battle more than the other European leagues, I guess.
Then again, I could be wrong about the league preparing PL teams for CL play because Tottenham hasn't even won in the league in what seems like forever, but somehow they're pulling off three-goal comebacks away from home. Maybe Pochettino just decided to focus on winning CL rather than to bother with getting top four.