Some history wrote:
In 1972 the standard was 2:30, then in 1976 they raised it to 2:28. That being said how may guys today can run under 2:30 or 2:28? A LOT. If those were the standards today then there were be a ton of guys going for it.
BTW, in 1972 and 1976 the US did pretty darn good at the Olympic marathon, the trials standard or other runners in the trials didn't seem to hurt them any.
The reason why the standards were so low back in 72 and 76 was because few people actually ran marathons back then.
Once everyone and his mother starting running the standard dropped fast, with a peak of 201 athletes making the 1984 standard of 2:19:04.
1972 2:30:00 100 Starters, 66 Finishers
1976 2:28:00 87 Qualifiers, 77 Starters, 49 Finishers
1980 2:21:54 225 Qualifiers, 192 Starters, 125 Finishers
1984 2:19:04 201 Qualifiers, 172 Starters, 108 Finishers
1988 2:20:00 136 Qualifiers, 115 Starters, 77 Finishers
1992 2:20:00 112 Qualifiers, 102 Starters, 55 Finishers
1996 2:20:00 (A); 2:22:00 (B) 135 Qualifiers, 116 Starters, 90 Finishers
2000 2:20:00 (A); 2:22:00 (B) 114 Qualifiers, 99 Starters, 78 Finishers