The reason is because it so much easier to sell the non-foil promo cards, so most players are aiming to earn 18-20 tickets, and even if you earned 20 on Day 1, getting another 70 is a tall feat, unless you have a way of combining tickets with friends/teammates
16 Toxrill, The Corrosive A Serious Threat With Little Escape Printed in Innistrad: Crimson Vow alongside Umbris, while Toxrill, the Corrosive may cost a hefty seven mana, once cast it is capable of single-handedly taking over a Commander game
If this happens, the ability will still resolve and you'll put a +1/+1 counter on Sharp-Eyed Rookie and investigate
The way its ability is worded also makes it so that you can choose not to do that, allowing you to use instants or key spells without worrying about sending them to the bottom of your library
Graded Population Report: Hydreigon ex #223 Visualize the distrbution of grades in the chart