I love good-quality natural fibres. And yes, a small percentage of synthetics (such as polyester or nylon) can make them a bit more hard wearing, more resistant to creasing, & increase longevity. Larger percentages, though, are usually to reduce costs ...
However, semi-synthetics (rayon - ie viscose/lyocell/modal), when mixed with natural fibres, also confer strength, resistance to creasing etc - & unlike natural/synthetic blends they remain fully biodegradable.
In fact, that's what Me+Em have done with their "Creaseless Linen" range - it's 53% linen & 47% viscose. There are, however, plenty of linen/viscose blends used by other clothing retailers, which will also be more resilient & resistant to wrinkling etc.