There is an old and bog standard form factor for SMT crystals – HC49/US.
The problem is that HC49/US takes a lot of real estate on the board. It's 12mm long.
Another problem with crystals and oscillators in general is that they often become long lead time items. [This is my experience.]
There are lots of small form factor crystals from various manufacturers. But, at a glance, it seems that there is no standardization of form factor. It’s nice when packages are standardized. It alleviates the long lead time problem. Crystals from manufacturer B may be used, if crystals from manufacturer A are out of stock.
Are there standard form factors for compact SMT crystals?
Armed with the insights from Gribo and Gustavo, I did a more focused survey. Found that 12MHz in 3.2×2.5mm package are produced by: Abracon, Citizen, Epson, Fox, ECS, TCS, NDK. To be included in this list, the part had to be in stock at DigiKey. It turns out that 3.2×2.5mm package is common across many manufacturers.