That is a known trait of frameless shower enclosures especially with curbless shower floors. They are not going to be as water tight as a framed glass enclosure with a curbed shower floor. However, an excessive amount of water outside of the shower could be do to the following assuming the shower picture shown is your shower or representative of your shower:

1. Your shower head is spraying directly towards the frameless sliding door opening where water can go through the vertical opening between the sliding and fixed glass as well as under the sliding glass. Typically a shower should be configured where the shower head is spraying towards a fixed portion of the glass and / or away from the door opening.
2. With the frameless slider there is no way to attach a frameless door seal or sweep. On a fixed frameless glass shower a vertical seal can be installed on the opening side and on the bottom of the door to minimize water leakage.
3. As already mentioned, the slope of your curbless shower floor may not be correct. The typical slope is 1/4" per foot (much easier to understand and measure than 1-2 degrees of slope.) To check this take a level and place it at the outer end of the shower floor to the drain and measure the distance from the level to the drain. In example, if the distance from the outer end of the shower floor is 3 ft. from the drain the drain should be a minimum of 3/4" (1/4" + 3 ft = 3/4") lower than the outer end of the shower floor.
4. Finally, although unlikely, your drain could either be two small or clogged. Typically the standard is a 2" drain pipe. If smaller (e.g. 1 1/2") or if clogged the amount of water coming out the shower head may be exceeding the drain flow capacity.