Why does it feel like these runes are completely worthless when behind

Celerity and Waterwalking don't really do much for you when you're pushed into your inhibitor towers while the enemy team still has all three of their outer towers

The Hunter runes all do nearly nothing if you aren't snowballing and carrying advantages to several lanes

The Legend runes are similar, requiring you to have already been in a winning position to stack properly

Dark Harvest and Grasp of the Undying similarly require being in winning positions to build up

Magical Footwear and other later pay off rune options require giving up early strength, which would be nice, if it didn't mean that characters that can dominate early while running these runes just turn them into free powerspikes after already bullying their way through laning.

Triumph literally negates the largest disincentive to bully out a single behind target by giving 25 extra gold no matter what their bounty, simultaneously adding very little extra reward for taking down opponents with a high bounty. Presence of mind is in a similar situation, letting snowballing characters mitigate any reason to back to base instead of just pressing their advantage more.

Future's Market enables spiking characters to get their broken items faster while setting back characters that might want to use it to stabilize.

Compare to the masteries of yore

Siegemaster allowed characters defending towers to get some extra leverage in the form of resistances

Fearless provided protection from large burst by similarly granting resistances to up-front damage while off cooldown

Legendary Guardian (The WORSE of its two mastery slot choices) granted bonus resitances when near a larger number of opponents, particularly relevant when defending against tower dives while playing safe

Bandit, not tied to support items, allowed hard lanes an out to get some amount of gold even when being forces off cs

It isn't just the lack of resistances early, the entire new rune system is full of snowbally messes and feast-or-famine mechanics that lead to every game being a roflstomp.