Cricket is nearly alone among major sports in having no standard field dimensions. That comes straight from where it was first played, on common land whose shape nobody controlled.
The common was whatever shape it was
Early matches happened on shared grazing land, village greens and open fields, none of which were laid out for sport or could be altered by the players.
The only part anyone prepared was the strip in the middle, because that is where the contest is decided and where a flat surface actually matters.
Everything beyond that strip was simply terrain. Trees, slopes and buildings became part of the ground rather than obstacles to be removed.
Boundaries were a later convenience
Originally a hit had to be run out, however far it traveled, and fielders chased the ball into whatever lay beyond the playing area.
Rope boundaries were introduced to stop disputes and to protect spectators, which meant the edge of the field became wherever the crowd happened to be standing.
Since crowds and enclosures differed at every ground, the boundary distance differed too, and the sport never had a moment where it could impose one number.
Asymmetry became a tactical feature
Because the pitch sits in the middle and batters face in both directions, one side of the ground is always shorter than the other for a given batter.
Captains set fields around that asymmetry, and batters target the short side deliberately, so a quirk of geography became a genuine layer of strategy.
Standardizing dimensions would remove that layer, which is part of why proposals to do so have never gained much support among players.
Historic grounds locked the variation in
Many famous grounds were built inside existing city blocks, on land bought piecemeal, and their outfields took the shape the property allowed.
Slopes, uneven ridges and short square boundaries survived because rebuilding the ground would mean losing the site, and the site is usually the more valuable asset.
Each ground therefore developed a reputation, and touring sides prepared for the venue as much as for the opposition, which is unusual in modern sport.
New stadiums quietly narrowed the range
Purpose-built venues, especially those shared with other sports, are drawn from a much narrower set of shapes, so boundary distances have converged without any rule change.
Drop-in surfaces and movable ropes push further in the same direction, letting organizers set the field to suit a broadcast rather than the land.
The variation that defined the sport is now a choice made by administrators rather than an inheritance from the ground, which is a different thing entirely.

