Buy more games, idle more cards.
Or check this thread for free keys > https://www.reddit.com/r/FreeGameFindings/new/

引用自 «Î||µmÏñå†üš»：

...So if it says "No more card drops remaining", I can't get anymore cards?

Yep.

Check your badges page and you'll see how many cards you can get.
Btw you don't need to download games to idle them.

"idling complete" means you don't have anything to drop.

Is there a limit to how many trading cards can drop?
Most games will drop a number of cards equal to about half the number of cards in that game's set of cards. For example, Half-Life 2 has 8 cards in its set, you can receive 4 card drops by playing it. You'll need to collect the other half of the set from other community members. Try the beta group discussions, community market, barter with friends, and trade discussions. You can check how many drops you have remaining on your badges page.

http://psteamcommunity.yuanyoumao.com/tradingcards/faq

What about free to play games like Team Fortress 2 or Dota 2?
Free to play games drop game cards based on your in-game purchasing. For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop. This card will drop at some point as you play. If you have made in-game purchases in Dota 2 or Team Fortress 2 prior to the Steam Trading Card Beta, or if you owned Team Fortress 2 prior to the Free to Play update, you will have 4 or 5 additional card drops available.

http://psteamcommunity.yuanyoumao.com/tradingcards/faq

引用自 Zu：

So i can use this safelly while not playing anything?

Yep.

http://psteamcommunity.yuanyoumao.com/groups/idlemastery/discussions/0/615085406651320102/

引用自 blyatiful # CSGOFade.net：

I owned Paladins too, shows 5 cards new to unlock, but nothing happens

For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop.

http://psteamcommunity.yuanyoumao.com/tradingcards/faq
What about free to play games like Team Fortress 2 or Dota 2?
Free to play games drop game cards based on your in-game purchasing. For every $9 USD spent (approximate) since the start of the Steam Trading Card Beta, you will earn one card drop. This card will drop at some point as you play. If you have made in-game purchases in Dota 2 or Team Fortress 2 prior to the Steam Trading Card Beta, or if you owned Team Fortress 2 prior to the Free to Play update, you will have 4 or 5 additional card drops available.

«Idling complete» means you're don't have available cards to drop. Check the FAQ > http://psteamcommunity.yuanyoumao.com/tradingcards/faq