Have you actually seen a legal doc that says they are exempt?
People can in general sell anything. Its the use that is mostly illegal.
Plus they can sell them as Agri legal & people use then for non agri illegally.
This is what I have found re IVA.
Article 2
Scope
1. This Directive applies to the type-approval of vehicles designed and constructed in one or more stages for use on the road, and of systems, components and separate technical units designed and constructed for such vehicles.
It also applies to the individual approval of such vehicles.
This Directive also applies to parts and equipment intended for vehicles covered by this Directive.
2. This Directive does not apply to the type-approval or individual approval of the following vehicles:
(a)
agricultural or forestry tractors, as defined in Directive 2003/37/EC of the European Parliament and of the Council of 26 May 2003 on type-approval of agricultural or forestry tractors, their trailers and interchangeable towed machinery, together with their systems, components and separate technical units (10) and trailers designed and constructed specifically to be towed by them;
(b)
quadricycles as defined in Directive 2002/24/EC of the European Parliament and of the Council of 18 March 2002 relating to the type-approval of two or three-wheel motor vehicles (11);
(c)
tracked vehicles.
3. Type-approval or individual approval under this Directive is optional for the following vehicles:
(a)
vehicles designed and constructed for use principally on construction sites or in quarries, port or airport facilities;
(b)
vehicles designed and constructed for use by the armed services, civil defence, fire services and forces responsible for maintaining public order; and
(c)
*****mobile machinery,*******
(seems to offer hope but see highlighted bit below)
to the extent that these vehicles fulfil the requirements of this Directive. Such optional approvals shall be without prejudice to the application of Directive 2006/42/EC of the European Parliament and of the Council of 17 May 2006 on machinery (12).
16.
‘mobile machinery’ means any self-propelled vehicle which is designed and constructed specifically to perform work which, because of its construction characteristics, is not suitable for carrying passengers or for transporting goods. Machinery mounted on a motor vehicle chassis shall not be considered as mobile machinery;
Quotes from here
https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A32007L0046